Dennis F Zaritsky

Interests

No activities entered.

Courses

Scholarly Contributions

Journals/Publications

• Zaritsky, D., Ting, Y., Tacchella, S., Speagle, J. S., Son, L. A., Naidu, R. P., Ji, A. P., Conroy, C., Chandra, V., Cargile, P., Caldwell, N., Broekgaarden, F. S., & Bonaca, A. (2022). Evidence from Disrupted Halo Dwarfs that r-process Enrichment via Neutron Star Mergers is Delayed by ≳500 Myr. The Astrophysical Journal Letters, 926(2), L36. doi:10.3847/2041-8213/ac5589
  More info

  Abstract The astrophysical origins of r-process elements remain elusive. Neutron star mergers (NSMs) and special classes of core-collapse supernovae (rCCSNe) are leading candidates. Due to these channels’ distinct characteristic timescales (rCCSNe: prompt, NSMs: delayed), measuring r-process enrichment in galaxies of similar mass but differing star formation durations might prove informative. Two recently discovered disrupted dwarfs in the Milky Way’s stellar halo, Kraken and Gaia-Sausage Enceladus (GSE), afford precisely this opportunity: Both have M ⋆ ≈ 108 M ⊙ but differing star formation durations of ≈2 Gyr and ≈3.6 Gyr. Here we present R ≈ 50,000 Magellan/MIKE spectroscopy for 31 stars from these systems, detecting the r-process element Eu in all stars. Stars from both systems have similar [Mg/H] ≈ −1, but Kraken has a median [Eu/Mg] ≈ −0.1 while GSE has an elevated [Eu/Mg] ≈ 0.2. With simple models, we argue NSM enrichment must be delayed by 500–1000 Myr to produce this difference. rCCSNe must also contribute, especially at early epochs, otherwise stars formed during the delay period would be Eu free. In this picture, rCCSNe account for ≈50% of the Eu in Kraken, ≈25% in GSE, and ≈15% in dwarfs with extended star formation durations like Sagittarius. The inferred delay time for NSM enrichment is 10×–100× longer than merger delay times from stellar population synthesis—this is not necessarily surprising because the enrichment delay includes time taken for NSM ejecta to be incorporated into subsequent generations of stars. For example, this may be due to natal kicks that result in r-enriched material deposited far from star-forming gas, which then takes ≈108–109 yr to cool in these galaxies.
• Zaritsky, D., Trujillo, I., Saifollahi, T., Peletier, R. F., Knapen, J. H., Donnerstein, R., Beasley, M. A., & Amorisco, N. (2022). Implications for galaxy formation models from observations of globular clusters around ultradiffuse galaxies. Monthly Notices of the Royal Astronomical Society, 511(3), 4633-4659. doi:10.1093/mnras/stac328
  More info

  ABSTRACT We present an analysis of Hubble Space Telescope observations of globular clusters (GCs) in six ultradiffuse galaxies (UDGs) in the Coma cluster, a sample that represents UDGs with large effective radii (Re), and use the results to evaluate competing formation models. We eliminate two significant sources of systematic uncertainty in the determination of the number of GCs, NGC by using sufficiently deep observations that (i) reach the turnover of the globular cluster luminosity function (GCLF) and (ii) provide a sufficient number of GCs with which to measure the GC number radial distribution. We find that NGC for these galaxies is on average ∼ 20, which implies an average total mass, Mtotal, ∼ 1011 M⊙ when applying the relation between NGC and Mtotal. This value of NGC lies at the upper end of the range observed for dwarf galaxies of the same stellar mass and is roughly a factor of two larger than the mean. The GCLF, radial profile, and average colour are more consistent with those observed for dwarf galaxies than with those observed for the more massive (L*) galaxies, while both the radial and azimuthal GC distributions closely follow those of the stars in the host galaxy. Finally, we discuss why our observations, specifically the GC number and GC distribution around these six UDGs, pose challenges for several of the currently favoured UDG formation models.
• Zaritsky, D., Zakamska, N. L., Ting, Y., Speagle, J. S., Hwang, H., Han, J. J., El-badry, K., Conroy, C., Chandra, V., Cargile, P., & Bonaca, A. (2022). Wide binaries from the H3 survey: The thick disk and halo have similar wide binary fractions. Monthly Notices of the Royal Astronomical Society. doi:10.1093/mnras/stac650
  More info

  Abstract Due to the different environments in the Milky Way’s disk and halo, comparing wide binaries in the disk and halo is key to understanding wide binary formation and evolution. By using Gaia Early Data Release 3, we search for resolved wide binary companions in the H3 survey, a spectroscopic survey that has compiled ∼150 000 spectra for thick-disk and halo stars to date. We identify 800 high-confidence (a contamination rate of 4 per cent) wide binaries and two resolved triples, with binary separations mostly between 103–105 AU and a lowest [Fe/H] of −2.7. Based on their Galactic kinematics, 33 of them are halo wide binaries, and most of those are associated with the accreted Gaia-Sausage-Enceladus galaxy. The wide binary fraction in the thick disk decreases toward the low metallicity end, consistent with the previous findings for the thin disk. Our key finding is that the halo wide binary fraction is consistent with the thick-disk stars at a fixed [Fe/H]. There is no significant dependence of the wide binary fraction on the α-captured abundance. Therefore, the wide binary fraction is mainly determined by the iron abundance, not their disk or halo origin nor the α-captured abundance. Our results suggest that the formation environments play a major role for the wide binary fraction, instead of other processes like radial migration that only apply to disk stars.
• Balogh, M. L., Burg, R. F., Muzzin, A., Rudnick, G., Wilson, G., Webb, K., Biviano, A., Boak, K., Cerulo, P., Chan, J., Cooper, M., Gilbank, D. G., Gwyn, S., Lidman, C., Matharu, J., McGee, S. L., Old, L., Pintos-Castro, I., Reeves, A. M., , Shipley, H., et al. (2021). The GOGREEN and GCLASS surveys: first data release. \mnras, 500(1), 358-387.
• Biviano, A., Burg, R., Balogh, M., Munari, E., Cooper, M., De Lucia, G., Demarco, R., Jablonka, P., Muzzin, A., Nantais, J., Old, L., Rudnick, G., Vulcani, B., Wilson, G., Yee, H., Zaritsky, D., Cerulo, P., Chan, J., Finoguenov, A., , Gilbank, D., et al. (2021). The GOGREEN survey: Internal dynamics of clusters of galaxies at redshift 0.9-1.4. \aap, 650, A105.
• Bonaca, A., Naidu, R. P., Conroy, C., Caldwell, N., Cargile, P. A., Han, J. J., Johnson, B. D., Kruijssen, J. D., Myeong, G., Speagle, J. S., Ting, Y., & Zaritsky, D. (2021). Orbital Clustering Identifies the Origins of Galactic Stellar Streams. \apjl, 909(2), L26.
• Carter, C., Conroy, C., Zaritsky, D., Ting, Y., Bonaca, A., Naidu, R. P., Johnson, B. D., Cargile, P. A., Caldwell, N., Speagle, J., & Han, J. J. (2021). Ancient Very Metal-poor Stars Associated with the Galactic Disk in the H3 Survey. \apj, 908(2), 208.
• Chan, J. C., Wilson, G., Balogh, M., Rudnick, G., Burg, R. F., Muzzin, A., Webb, K. A., Biviano, A., Cerulo, P., Cooper, M., De, L. G., Demarco, R., Forrest, B., Jablonka, P., Lidman, C., McGee, S. L., Nantais, J., Old, L., Pintos-Castro, I., , Poggianti, B., et al. (2021). The GOGREEN Survey: Evidence of an Excess of Quiescent Disks in Clusters at 1.0. \apj, 920(1), 32.
• Conroy, C., Naidu, R. P., Garavito-Camargo, N., Besla, G., Zaritsky, D., Bonaca, A., & Johnson, B. D. (2021). All-sky dynamical response of the Galactic halo to the Large Magellanic Cloud. \nat, 592(7855), 534-536.
• Gonzalez, A. H., George, T., Connor, T., Deason, A., Donahue, M., Montes, M., Zabludoff, A. I., & Zaritsky, D. (2021). Discovery of a possible splashback feature in the intracluster light of MACS J1149.5+2223. \mnras, 507(1), 963-970.
• Jones, M. G., Bennet, P., Mutlu-Pakdil, B., Sand, D. J., Spekkens, K., Crnojevi{\'c}, D., Karunakaran, A., & Zaritsky, D. (2021). Evidence for Ultra-diffuse Galaxy Formation through Tidal Heating of Normal Dwarfs. \apj, 919(2), 72.
• Kadowaki, J., Zaritsky, D., Donnerstein, R., RS, P., Karunakaran, A., & Spekkens, K. (2021). On the Properties of Spectroscopically Confirmed Ultra-diffuse Galaxies across Environments. \apj, 923(2), 257.
• Karunakaran, A., Spekkens, K., Oman, K. A., Simpson, C. M., Fattahi, A., Sand, D. J., Bennet, P., Crnojevi{\'c}, D., Frenk, C. S., G{\'omez}, F. A., Grand, R. J., Jones, M. G., Marinacci, F., Mutlu-Pakdil, B., Navarro, J. F., & Zaritsky, D. (2021). Satellites around Milky Way Analogs: Tension in the Number and Fraction of Quiescent Satellites Seen in Observations versus Simulations. \apjl, 916(2), L19.
• McNab, K., Balogh, M. L., Burg, R. F., Forestell, A., Webb, K., Vulcani, B., Rudnick, G., Muzzin, A., Cooper, M., McGee, S., Biviano, A., Cerulo, P., Chan, J. C., De, L. G., Demarco, R., Finoguenov, A., Forrest, B., Golledge, C., Jablonka, P., , Lidman, C., et al. (2021). The GOGREEN survey: transition galaxies and the evolution of environmental quenching. \mnras, 508(1), 157-174.
• Naidu, R. P., Conroy, C., Bonaca, A., Zaritsky, D., Weinberger, R., Ting, Y., Caldwell, N., Tacchella, S., Han, J. J., Speagle, J. S., & Cargile, P. A. (2021). Reconstructing the Last Major Merger of the Milky Way with the H3 Survey. \apj, 923(1), 92.
• Nidever, D. L., Olsen, K., Choi, Y., Ruiz-Lara, T., Miller, A. E., Johnson, L. C., Bell, C. P., Blum, R. D., Cioni, M. L., Gallart, C., Majewski, S. R., Martin, N. F., Massana, P., Monachesi, A., No{\"el}, N. E., Sakowska, J. D., Marel, R. P., Walker, A. R., Zaritsky, D., , Bell, E. F., et al. (2021). The Second Data Release of the Survey of the MAgellanic Stellar History (SMASH). \aj, 161(2), 74.
• Reeves, A. M., Balogh, M. L., Burg, R. F., Finoguenov, A., Kukstas, E., McCarthy, I. G., Webb, K., Muzzin, A., McGee, S., Rudnick, G., Biviano, A., Cerulo, P., Chan, J. C., Cooper, M., Demarco, R., Jablonka, P., De, L. G., Vulcani, B., Wilson, G., , Yee, H. K., et al. (2021). The GOGREEN survey: dependence of galaxy properties on halo mass at z > 1 and implications for environmental quenching. \mnras, 506(3), 3364-3384.
• Sp{\'erone-Longin}, D., Jablonka, P., Combes, F., Castignani, G., Krips, M., Rudnick, G., Desjardins, T., Zaritsky, D., Finn, R., De Lucia, G., & Desai, V. (2021). SEEDisCS. II. Molecular gas in galaxy clusters and their large-scale structure: low gas fraction galaxies, the case of CL1301.7\ensuremath{-}1139. \aap, 654, A69.
• Sp{\'erone-Longin}, D., Jablonka, P., Combes, F., Castignani, G., Krips, M., Rudnick, G., Zaritsky, D., Finn, R., De Lucia, G., & Desai, V. (2021). SEEDisCS. I. Molecular gas in galaxy clusters and their large-scale structure: The case of CL1411.1\ensuremath{-}1148 at z \ensuremath{\sim} 0.5. \aap, 647, A156.
• Trujillo, I., D'Onofrio, M., Zaritsky, D., Madrigal-Aguado, A., Chamba, N., Golini, G., Akhlaghi, M., Sharbaf, Z., Infante-Sainz, R., Rom{\'an}, J., Morales-Socorro, C., Sand, D. J., & Martin, G. (2021). Introducing the LBT Imaging of Galactic Halos and Tidal Structures (LIGHTS) survey. A preview of the low surface brightness Universe to be unveiled by LSST. \aap, 654, A40.
• Zaritsky, D., Donnerstein, R., Karunakaran, A., Barbosa, C., Dey, A., Kadowaki, J., Spekkens, K., & Zhang, H. (2021). Systematically Measuring Ultra-diffuse Galaxies (SMUDGes). II. Expanded Survey Description and the Stripe 82 Catalog. \apjs, 257(2), 60.
• Zaritsky, D., Trujillo, I., Sharbaf, Z., Sand, D. J., Roman, J., Morales-socorro, C., Martin, G., Madrigal-aguado, A., Infante-sainz, R., Golini, G., D'onofrio, M., Chamba, N., & Akhlaghi, M. (2021). Introducing the LBT Imaging of Galactic Halos and Tidal Structures (LIGHTS) survey. Astronomy & Astrophysics, 654, A40. doi:10.1051/0004-6361/202141603
  More info

  We present the first results of the LBT Imaging of Galaxy Haloes and Tidal Structures (LIGHTS) survey. LIGHTS is an ongoing observational campaign with the 2 × 8.4 m Large Binocular Telescope (LBT) aiming to explore the stellar haloes and the low surface brightness population of satellites down to a depth of μV ∼ 31 mag arcsec−2 (3σ in 10″ × 10″ boxes) of nearby galaxies. We simultaneously collected deep imaging in the g and r Sloan filters using the Large Binocular Cameras. The resulting images are 60 times (i.e. ∼4.5 mag) deeper than those from the Sloan Digital Sky Survey, and they have characteristics comparable (in depth and spatial resolution) to the ones expected from the future Legacy Survey of Space and Time (LSST). Here we show the first results of our pilot programme targeting NGC 1042 (an M 33 analogue at a distance of 13.5 Mpc) and its surroundings. The depth of the images allowed us to detect an asymmetric stellar halo in the outskirts of this galaxy whose mass (1.4 ± 0.4 × 108 M⊙) is in agreement with the ΛCDM expectations. Additionally, we show that deep imaging from the LBT reveals low mass satellites (a few times 105 M⊙) with very faint central surface brightness μV(0) ∼ 27 mag arcsec−2 (i.e. similar to Local Group dwarf spheroidals, such as Andromeda XIV or Sextans, but at distances well beyond the local volume). The depth and spatial resolution provided by the LIGHTS survey open up a unique opportunity to explore the ‘missing satellites’ problem in a large variety of galaxies beyond our Local Group down to masses where the difference between the theory and observation (if any) should be significant.
• Zaritsky, D., Weiner, B. J., Vulcani, B., Teplitz, H. I., Sperone-longin, D., Rudnick, G. H., Moustakas, J., Mann, J. L., Jaffe, Y. L., Jablonka, P., Finn, R. A., De lucia, G., Desjardins, T., Desai, V., Cooper, J. R., Brammer, G. G., & Aragon-salamanca, A. (2021). H α-based star formation rates in and around z ∼ 0.5 EDisCS clusters. Monthly Notices of the Royal Astronomical Society, 509(4), 5382-5398. doi:10.1093/mnras/stab3184
  More info

  ABSTRACT We investigate the role of environment on star formation rates (SFRs) of galaxies at various cosmic densities in well-studied clusters. We present the star-forming main sequence for 163 galaxies in four EDisCS clusters in the range 0.4 < z < 0.7. We use Hubble Space Telescope/Wide Field Camera 3 observations of the H α emission line to span three distinct local environments: the cluster core, infall region, and external field galaxies. The main sequence defined from our observations is consistent with other published H α distributions at similar redshifts but differs from those derived from star formation tracers such as 24 $\, \mu$m. We find that the Hα-derived SFRs for the 67 galaxies with stellar masses greater than the mass-completeness limit of M* > 109.75 M⊙ show little dependence on environment. At face value, the similarities in the SFR distributions in the three environments may indicate that the process of finally shutting down star formation is rapid, however, the depth of our data and size of our sample make it difficult to conclusively test this scenario. Despite having significant H α emission, 21 galaxies are classified as UVJ-quiescent and may represent a demonstration of the quenching of star formation caught in the act.
• Zhang, H., Zaritsky, D., Olsen, K. P., Behroozi, P., Werk, J., Kennicutt, R., Xie, L., Yang, X., Fang, T., De, L. G., Hirschmann, M., & Fontanot, F. (2021). An Empirical Determination of the Dependence of the Circumgalactic Mass Cooling Rate and Feedback Mass Loading Factor on Galactic Stellar Mass. \apj, 916(2), 101.
• Barbosa, C., Zaritsky, D., Donnerstein, R., Zhang, H., Dey, A., Oliveira, C., Sampedro, L., Molino, A., Costa-Duarte, M., Coelho, P., Cortesi, A., Herpich, F., Hernandez-Jimenez, J., Santos-Silva, T. .., Pereira, E., Werle, A., Overzier, R., Cid Fernandes, R., Smith, C. A., , Ribeiro, T., et al. (2020). One Hundred SMUDGes in S-PLUS: Ultra-diffuse Galaxies Flourish in the Field. \apjs, 247(2), 46.
• Bell, C. P., Cioni, M. L., Wright, A., Rubele, S., Nidever, D. L., Tatton, B. L., Loon, J. T., Zaritsky, D., Choi, Y., Choudhury, S., Clementini, G., Grijs, R., Ivanov, V. D., Majewski, S. R., Marconi, M., Mart{\'\inez-Delgado}, D., Massana, P., Mu{\~noz}, R. R., Niederhofer, F., , No{\"el}, N. E., et al. (2020). The intrinsic reddening of the Magellanic Clouds as traced by background galaxies - II. The Small Magellanic Cloud. \mnras, 499(1), 993-1004.
• Bennet, P., Sand, D., Crnojevi{\'c}, D., Spekkens, K., Karunakaran, A., Zaritsky, D., & Mutlu-Pakdil, B. .. (2020). The Satellite Luminosity Function of M101 into the Ultra-faint Dwarf Galaxy Regime. \apjl, 893(1), L9.
• Bonaca, A., Conroy, C., Cargile, P. A., Naidu, R. P., Johnson, B. D., Zaritsky, D., Ting, Y., Caldwell, N., Han, J. J., & Dokkum, P. (2020). Timing the Early Assembly of the Milky Way with the H3 Survey. \apjl, 897(1), L18.
• Burg, R. F., Rudnick, G., Balogh, M. L., Muzzin, A., Lidman, C., Old, L. J., Shipley, H., Gilbank, D., McGee, S., Biviano, A., Cerulo, P., Chan, J. C., Cooper, M., De, L. G., Demarco, R., Forrest, B., Gwyn, S., Jablonka, P., Kukstas, E., , Marchesini, D., et al. (2020). The GOGREEN Survey: A deep stellar mass function of cluster galaxies at 1.0 < z < 1.4 and the complex nature of satellite quenching. \aap, 638, A112.
• DeMaio, T., Gonzalez, A. H., Zabludoff, A., Zaritsky, D., Aldering, G., Brodwin, M., Connor, T., Donahue, M., Hayden, B., Mulchaey, J. S., Perlmutter, S., & Stanford, S. (2020). The growth of brightest cluster galaxies and intracluster light over the past 10 billion years. \mnras, 491(3), 3751-3759.
• Johnson, B. D., Conroy, C., Naidu, R. P., Bonaca, A., Zaritsky, D., Ting, Y., Cargile, P. A., Han, J. J., & Speagle, J. S. (2020). A Diffuse Metal-poor Component of the Sagittarius Stream Revealed by the H3 Survey. \apj, 900(2), 103.
• Karunakaran, A., Spekkens, K., Bennet, P., Sand, D., Crnojevi{\'c}, D., & Zaritsky, D. (2020). Neutral Hydrogen Observations of Low Surface Brightness Galaxies around M101 and NGC 5485. \aj, 159(2), 37.
• Karunakaran, A., Spekkens, K., Zaritsky, D., Donnerstein, R. L., Kadowaki, J., & Dey, A. (2020). Systematically Measuring Ultradiffuse Galaxies in H I: Results from the Pilot Survey. \apj, 902(1), 39.
• Massana, P., No{\"el}, N. E., Nidever, D. L., Erkal, D., Boer, T. J., Choi, Y., Majewski, S. R., Olsen, K., Monachesi, A., Gallart, C., Marel, R. P., Ruiz-Lara, T., Zaritsky, D., Martin, N. F., Mu{\~noz}, R. R., Cioni, M. L., Bell, C. P., Bell, E. F., Stringfellow, G. S., , Belokurov, V., et al. (2020). SMASHing the low surface brightness SMC. \mnras, 498(1), 1034-1049.
• Mutlu-Pakdil, B., Sand, D. J., Crnojevi{\'c}, D., Olszewski, E. W., Zaritsky, D., Strader, J., Collins, M. L., Seth, A. C., & Willman, B. (2020). The Elusive Distance Gradient in the Ultrafaint Dwarf Galaxy Hercules: A Combined Hubble Space Telescope and Gaia View. \apj, 902(2), 106.
• Naidu, R. P., Conroy, C., Bonaca, A., Johnson, B. D., Ting, Y., Caldwell, N., Zaritsky, D., & Cargile, P. A. (2020). Evidence from the H3 Survey That the Stellar Halo Is Entirely Comprised of Substructure. \apj, 901(1), 48.
• Old, L. J., Balogh, M. L., Burg, R. F., Biviano, A., Yee, H. K., Pintos-Castro, I., Webb, K., Muzzin, A., Rudnick, G., Vulcani, B., Poggianti, B., Cooper, M., Zaritsky, D., Cerulo, P., Wilson, G., Chan, J. C., Lidman, C., McGee, S., Demarco, R., , Forrest, B., et al. (2020). The GOGREEN survey: the environmental dependence of the star-forming galaxy main sequence at 1.0 < z < 1.5. \mnras, 493(4), 5987-6000.
• Ruiz-Lara, T. .., Gallart, C., Monelli, M., Nidever, D., Dorta, A., Choi, Y., Olsen, K., Besla, G., Bernard, E., Cassisi, S., Massana, P., No{\"el}, N., P{\'erez}, I., Rusakov, V., Cioni, M. -., Majewski, S., Marel, R., Mart{\'\inez-Delgado}, D., Monachesi, A., , Monteagudo, L., et al. (2020). The Large Magellanic Cloud stellar content with SMASH. I. Assessing the stability of the Magellanic spiral arms. \aap, 639, L3.
• Webb, K., Balogh, M. L., Leja, J., Burg, R. F., Rudnick, G., Muzzin, A., Boak, K., Cerulo, P., Gilbank, D., Lidman, C., Old, L. J., Pintos-Castro, I., McGee, S., Shipley, H., Biviano, A., Chan, J. C., Cooper, M., De, L. G., Demarco, R., , Forrest, B., et al. (2020). The GOGREEN survey: post-infall environmental quenching fails to predict the observed age difference between quiescent field and cluster galaxies at z > 1. \mnras, 498(4), 5317-5342.
• Zaritsky, D., Conroy, C., Naidu, R. P., Cargile, P. A., Putman, M., Besla, G., Bonaca, A., Caldwell, N., Han, J. J., Johnson, B. D., Speagle, J. S., & Ting, Y. (2020). Discovery of Magellanic Stellar Debris in the H3 Survey. \apjl, 905(1), L3.
• Zaritsky, D., Conroy, C., Zhang, H., Naidu, R. P., Bonaca, A., Caldwell, N., Cargile, P. A., & Johnson, B. D. (2020). A Lower Limit on the Mass of Our Galaxy from the H3 Survey. \apj, 888(2), 114.
• Zaritsky, D., Yee, H. K., Wilson, G., Webb, T., Webb, K., Vulcani, B., Valotto, C., Townsend, M., Shipley, H., Rudnick, G., Reeves, A. M., Poggianti, B. M., Pintos-castro, I., Petter, G. C., Parker, L. C., Old, L., Noble, A., Nantais, J., Muzzin, A., , Muriel, H., et al. (2020). The GOGREEN and GCLASS surveys : first data release. Monthly Notices of the Royal Astronomical Society, 500(1), 358-387. doi:10.1093/mnras/staa3008
  More info

  We present the first public data release of the GOGREEN and GCLASS surveys of galaxies in dense environments, spanning a redshift range $0.8
• Zaritsky, D., Yee, H. K., Wilson, G., Webb, T., Webb, K., Vulcani, B., Van der burg, R. F., Valotto, C. A., Townsend, M., Shipley, H., Rudnick, G., Reeves, A. M., Poggianti, B. M., Pintos-castro, I., Petter, G. C., Parker, L. C., Old, L., Noble, A., Nantais, J. B., , Muzzin, A., et al. (2020). The GOGREEN and GCLASS surveys: first data release. Monthly Notices of the Royal Astronomical Society, 500(1), 358-387. doi:10.1093/mnras/staa3008
  More info

  We present the first public data release of the GOGREEN and GCLASS surveys of galaxies in dense environments, spanning a redshift range $0.8
• Zhang, H., Fang, T., Zaritsky, D., Behroozi, P., Werk, J., & Yang, X. (2020). Observing the Effects of Galaxy Interactions on the Circumgalactic Medium. \apjl, 893(1), L3.
• Zhang, H., Yang, X., Zaritsky, D., Behroozi, P., & Werk, J. (2020). H\ensuremath{\alpha} Emission and the Dependence of the Circumgalactic Cool Gas Fraction on Halo Mass. \apj, 888(1), 33.
• Bell, C., Cioni, M. L., Wright, A. H., Rubele, S., Nidever, D. L., Tatton, B. L., van, L., Ivanov, V. D., Subramanian, S., Oliveira, J. M., de, G. R., Pennock, C. M., Choi, Y., Zaritsky, D., Olsen, K., Niederhofer, F., Choudhury, S., Martinez-Delgado, D., & Munoz, R. R. (2019). The intrinsic reddening of the Magellanic Clouds as traced by background galaxies - I. The bar and outskirts of the Small Magellanic Cloud. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 489(3), 3200-3217.
• Bennet, P., Sand, D. J., Crnojevic, D., Spekkens, K., Karunakaran, A., Zaritsky, D., & Mutlu-Pakdil, B. (2019). The M101 Satellite Luminosity Function and the Halo?Halo Scatter among Local Volume Hosts. ASTROPHYSICAL JOURNAL, 885(2).
• Blum, R. D., Besla, G., Zivick, P., Zaritsky, D., Walker, A. R., Vivas, A. K., Stringfellow, G. S., Seibert, M., Schmidt, J., Pieres, A., Olsen, K., Noel, N. E., Nidever, D. L., Neyer, F., Munoz, R. R., Monteagudo, L., Monelli, M., Martinez-delgado, D., Martin, N. F., , Marel, R. P., et al. (2019). Nature of a shell of young stars in the outskirts of the Small Magellanic Cloud. Astronomy and Astrophysics, 631, A98. doi:10.1051/0004-6361/201936021
  More info

  Context. Understanding the evolutionary history of the Magellanic Clouds requires an in-depth exploration and characterization of the stellar content in their outer regions, which ultimately are key to tracing the epochs and nature of past interactions. Aims. We present new deep images of a shell-like overdensity of stars in the outskirts of the Small Magellanic Cloud (SMC). The shell, also detected in photographic plates dating back to the fifties, is located at ∼1.9° from the center of the SMC in the north-east direction. Methods. The structure and stellar content of this feature were studied with multiband, optical data from the Survey of the MAgellanic Stellar History (SMASH) carried out with the Dark Energy Camera on the Blanco Telescope at Cerro Tololo Inter-American Observatory. We also investigate the kinematic of the stars in the shell using the Gaia Data Release 2. Results. The shell is composed of a young population with an age ∼150 Myr, with no contribution from an old population. Thus, it is hard to explain its origin as the remnant of a tidally disrupted stellar system. The spatial distribution of the young main-sequence stars shows a rich sub-structure, with a spiral arm-like feature emanating from the main shell and a separated small arc of young stars close to the globular cluster NGC 362. We find that the absolute g-band magnitude of the shell is Mg, shell = −10.78 ± 0.02, with a surface brightness of μg, shell = 25.81 ± 0.01 mag arcsec−2. Conclusion. We have not found any evidence that this feature is of tidal origin or a bright part of a spiral arm-like structure. Instead, we suggest that the shell formed in a recent star formation event, likely triggered by an interaction with the Large Magellanic Cloud and or the Milky Way, ∼150 Myr ago.
• Chan, J., Wilson, G., Rudnick, G., Muzzin, A., Balogh, M., Nantais, J., van, d., Cerulo, P., Biviano, A., Cooper, M. C., Demarco, R., Forrest, B., Lidman, C., Noble, A., Old, L., Pintos-Castro, I., Reeves, A., Webb, K. A., Yee, H., , Abdullah, M. H., et al. (2019). The Rest-frame H-band Luminosity Function of Red-sequence Galaxies in Clusters at 1.0 < Z < 1.3. ASTROPHYSICAL JOURNAL, 880(2).
• Conroy, C., Bonaca, A., Cargile, P., Johnson, B. D., Caldwell, N., Naidu, R. P., Zaritsky, D., Fabricant, D., Moran, S., Rhee, J., Szentgyorgyi, A., Berlind, P., Calkins, M. L., Kattner, S., & Ly, C. (2019). Mapping the Stellar Halo with the H3 Spectroscopic Survey. ASTROPHYSICAL JOURNAL, 883(1).
• Conroy, C., Naidu, R. P., Zaritsky, D., Bonaca, A., Cargile, P., Johnson, B. D., & Caldwell, N. (2019). Resolving the Metallicity Distribution of the Stellar Halo with the H3 Survey. ASTROPHYSICAL JOURNAL, 887(2).
• Dey, A., Schlegel, D. J., Lang, D., Blum, R., Burleigh, K., Fan, X., Findlay, J. R., Finkbeiner, D., Herrera, D., Juneau, S., Landriau, M., Levi, M., McGreer, I., Meisner, A., Myers, A. D., Moustakas, J., Nugent, P., Patej, A., Schlafly, E. F., , Walker, A. R., et al. (2019). Overview of the DESI Legacy Imaging Surveys. ASTRONOMICAL JOURNAL, 157(5).
• Hamden, E. T., Tuttle, S., Tumlinson, J., Tripp, T. M., Tremblay, G. R., Tollerud, E. J., Strom, A. L., Stern, J., Snyder, G. F., Simons, R. C., Shapley, A. E., Scarlata, C., Salmon, B., Rubin, K. H., Rowlands, K., Ribaudo, J., Rafelski, M., Quataert, E., Putman, M. E., , Prescott, M. K., et al. (2019). Understanding the circumgalactic medium is critical for understanding galaxy evolution. Bulletin of the American Astronomical Society, 51(3).
  More info

  Author(s): Peeples, Molly S; Behroozi, Peter; Bordoloi, Rongmon; Brooks, Alyson; Bullock, James S; Burchett, Joseph N; Chen, Hsiao-Wen; Chisholm, John; Christensen, Charlotte; Coil, Alison; Corlies, Lauren; Diamond-Stanic, Aleksandar; Donahue, Megan; Faucher-Giguere, Claude-Andre; Ferguson, Henry; Fielding, Drummond; Fox, Andrew J; French, David M; Furlanetto, Steven R; Gennaro, Mario; Gilbert, Karoline M; Hamden, Erika; Hathi, Nimish; Hayes, Matthew; Henry, Alaina; Howk, J Christopher; Hummels, Cameron; Keres, Dusan; Kirby, Evan; Koekemoer, Anton M; Lan, Ting-Wen; Lanz, Lauranne; Law, David R; Lehner, Nicolas; Lotz, Jennifer M; Martin, Crystal L; McQuinn, Kristen; McQuinn, Matthew; Munshi, Ferah; Oh, S Peng; O'Meara, John M; O'Shea, Brian W; Pacifici, Camilla; Peek, JEG; Postman, Marc; Prescott, Moire; Putman, Mary; Quataert, Eliot; Rafelski, Marc; Ribaudo, Joseph; Rowlands, Kate; Rubin, Kate; Salmon, Brett; Scarlata, Claudia; Shapley, Alice E; Simons, Raymond; Snyder, Gregory F; Stern, Jonathan; Strom, Allison L; Tollerud, Erik; Torrey, Paul; Tremblay, Grant; Tripp, Todd M; Tumlinson, Jason; Tuttle, Sarah; Bosch, Frank C van den; Voit, G Mark; Wang, Q Daniel; Werk, Jessica K; Williams, Benjamin F; Zaritsky, Dennis; Zheng, Yong | Abstract: Galaxies evolve under the influence of gas flows between their interstellar medium and their surrounding gaseous halos known as the circumgalactic medium (CGM). The CGM is a major reservoir of galactic baryons and metals, and plays a key role in the long cycles of accretion, feedback, and recycling of gas that drive star formation. In order to fully understand the physical processes at work within galaxies, it is therefore essential to have a firm understanding of the composition, structure, kinematics, thermodynamics, and evolution of the CGM. In this white paper we outline connections between the CGM and galactic star formation histories, internal kinematics, chemical evolution, quenching, satellite evolution, dark matter halo occupation, and the reionization of the larger-scale intergalactic medium in light of the advances that will be made on these topics in the 2020s. We argue that, in the next decade, fundamental progress on all of these major issues depends critically on improved empirical characterization and theoretical understanding of the CGM. In particular, we discuss how future advances in spatially-resolved CGM observations at high spectral resolution, broader characterization of the CGM across galaxy mass and redshift, and expected breakthroughs in cosmological hydrodynamic simulations will help resolve these major problems in galaxy evolution.
• Just, D. W., Kirby, M., Zaritsky, D., Rudnick, G., Desjardins, T., Cool, R., Moustakas, J., Clowe, D., De, L. G., Aragon-Salamanca, A., Desai, V., Finn, R., Halliday, C., Jablonka, P., Mann, J., Poggianti, B., Bian, F., & Liebst, K. (2019). Preprocessing among the Infalling Galaxy Population of EDisCS Clusters. ASTROPHYSICAL JOURNAL, 885(1).
• Mendes, d., Ribeiro, T., Schoenell, W., Kanaan, A., Overzier, R. A., Molino, A., Sampedro, L., Coelho, P., Barbosa, C. E., Cortesi, A., Costa-Duarte, M. V., Herpich, F. R., Hernandez-Jimenez, J. A., Placco, V. M., Xavier, H. S., Abramo, L. R., Saito, R. K., Chies-Santos, A. L., Ederoclite, A., , Lopes, d., et al. (2019). The Southern Photometric Local Universe Survey (S-PLUS): improved SEDs, morphologies, and redshifts with 12 optical filters. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 489(1), 241-267.
• Mutlu-Pakdil, B., Sand, D. J., Walker, M. G., Caldwell, N., Carlin, J. L., Collins, M. L., Crnojevic, D., Mateo, M., Olszewski, E. W., Seth, A. C., Strader, J., Willman, B., & Zaritsky, D. (2019). Signatures of Tidal Disruption in Ultra-faint Dwarf Galaxies: A Combined HST, Gaia, and MMT/Hectochelle Study of Leo V. ASTROPHYSICAL JOURNAL, 885(1).
• Nidever, D. L., Olsen, K., Choi, Y., de, B., Blum, R. D., Bell, E. F., Zaritsky, D., Martin, N. F., Saha, A., Conn, B. C., Besla, G., van, d., Noel, N., Monachesi, A., Stringfellow, G. S., Massana, P., Cioni, M. L., Gallart, C., Monelli, M., , Martinez-Delgado, D., et al. (2019). Exploring the Very Extended Low-surface-brightness Stellar Populations of the Large Magellanic Cloud with SMASH. ASTROPHYSICAL JOURNAL, 874(2).
• Park, H. S., Moon, D., Zaritsky, D., Kim, S. C., Lee, Y., Cha, S., & Lee, Y. (2019). Dwarf Galaxy Discoveries from the KMTNet Supernova Program. II. The NGC 3585 Group and Its Dynamical State** Based on data collected at the KMTNet Telescopes.. ASTROPHYSICAL JOURNAL, 885(1).
• Rossi, S., Trevisan, M., Nakazono, L. M., Oliveira, A. S., Almeida, L. A., Schoenell, W., Daflon, S., Saito, R. K., Santos, R. B., Overzier, R. A., Dupke, R. A., Zaritsky, D., Xavier, H. S., Whitten, D. D., Westera, P., Werner, S. V., Werle, A., Vitorelli, A. Z., Vika, M., , Veiga, C. H., et al. (2019). A new sample of southern radio galaxies: Host galaxy masses and star-formation rates. Monthly Notices of the Royal Astronomical Society, 489, 241-267. doi:10.1093/mnras/stz2371
• Singh, P. R., Zaritsky, D., Donnerstein, R., & Spekkens, K. (2019). Ultra-diffuse Galaxies at Ultraviolet Wavelengths. ASTRONOMICAL JOURNAL, 157(5).
• Zaritsky, D., Donnerstein, R., Dey, A., Kadowaki, J., Zhang, H., Karunakaran, A., Martinez-Delgado, D., Rahman, M., & Spekkens, K. (2019). Systematically Measuring Ultra-diffuse Galaxies (SMUDGes). I. Survey Description and First Results in the Coma Galaxy Cluster and Environs. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 240(1).
• Zaritsky, D., Werk, J. K., Wang, Q. D., Tumlinson, J., Rafelski, M., Peeples, M. S., Peek, J. E., O'meara, J. M., Lehner, N., & Burchett, J. N. (2019). The Panchromatic Circumgalactic Medium. Bulletin of the American Astronomical Society, 51(3).
  More info

  Galaxies are surrounded by extended atmospheres, which are often called the circumgalactic medium (CGM) and are the least understood part of galactic ecosystems. The CGM serves as a reservoir of both diffuse, metal-poor gas accreted from the intergalactic medium, and metal-rich gas that is either ejected from galaxies by energetic feedback or stripped from infalling satellites. As such, the CGM is empirically multi-phased and complex in dynamics. Significant progress has been made in the past decade or so in observing the cosmic-ray/B-field, as well as various phases of the CGM. But basic questions remain to be answered. First, what are the energy, mass, and metal contents of the CGM? More specifically, how are they spatially distributed and partitioned in the different components? Moreover, how are they linked to properties of host galaxies and their global clustering and intergalactic medium environments? Lastly, what are the origin, state, and life-cycle of the CGM? This question explores the dynamics of the CGM. Here we illustrate how these questions may be addressed with multi-wavelength observations of the CGM.
• Zhang, H., Zaritsky, D., Behroozi, P., & Werk, J. (2019). On the Effect of Environment on Line Emission from the Circumgalactic Medium. ASTROPHYSICAL JOURNAL, 880(1).
• Zhang, H., Zaritsky, D., Ly, C., Zhang, H., Zaritsky, D., Zabludoff, A. I., Woodrum, C., Wechsler, R. H., Wang, Y., Tollerud, E. J., Tinker, J. L., Somerville, R. S., Rodriguez, A., Papovich, C., O'donnell, C., Moster, B. P., Mao, Y., Ly, C., Leauthaud, A., , Hirata, C. M., et al. (2019). Empirically Constraining Galaxy Evolution. Bulletin of the American Astronomical Society, 51(3).
  More info

  Empirical models of galaxy formation have demonstrated both significant successes and significant promise for the next decade.
• Zhang, H., Zaritsky, D., Zhang, H., Zaritsky, D., Werk, J. K., Tuttle, S., Peeples, M. S., & Behroozi, P. (2019). Emission Line Mapping of the Circumgalactic Medium of Nearby Galaxies. Bulletin of the American Astronomical Society, 51(3).
  More info

  The circumgalactic medium (CGM), which harbors > 50% of all the baryons in a galaxy, is both the reservoir of gas for subsequent star formation and the depository of chemically processed gas, energy, and angular momentum from feedback. As such, the CGM obviously plays a critical role in galaxy evolution. We discuss the opportunity to image this component using recombination line emission, beginning with the early results coming from recent statistical detection of this emission to the final goal of realizing spectral-line images of the CGM in individual nearby galaxies. Such work will happen in the next decade and provide new insights on the galactic baryon cycle.
• Bennet, P., Sand, D. J., Zaritsky, D., Crnojevic, D., Spekkens, K., & Karunakaran, A. (2018). Evidence for Ultra-diffuse Galaxy "Formation" through Galaxy Interactions. ASTROPHYSICAL JOURNAL LETTERS, 866(1).
• Bitsakis, T., Gonzalez-Lopezlira, R. A., Bonfini, P., Bruzual, G., Maravelias, G., Zaritsky, D., Charlot, S., & Ramirez-Siordia, V. H. (2018). The Distribution and Ages of Star Clusters in the Small Magellanic Cloud: Constraints on the Interaction History of the Magellanic Clouds. ASTROPHYSICAL JOURNAL, 853(2).
• Bouquin, A., de, P., Carlos, M. J., Boissier, S., Sheth, K., Zaritsky, D., Peletier, R. F., Knapen, J. H., & Gallego, J. (2018). The GALEX/S(4)G Surface Brightness and Color Profiles Catalog. I. Surface Photometry and Color Gradients of Galaxies. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 234(2).
• Choi, Y., Nidever, D. L., Olsen, K., Besla, G., Blum, R. D., Zaritsky, D., Cioni, M. L., van, d., Bell, E. F., Johnson, L. C., Katherina, V. A., Walker, A. R., de, B., Noel, N., Monachesi, A., Gallart, C., Monelli, M., Stringfellow, G. S., Massana, P., , Martinez-Delgado, D., et al. (2018). SMASHing the LMC: Mapping a Ring-like Stellar Overdensity in the LMC Disk. ASTROPHYSICAL JOURNAL, 869(2).
• Choi, Y., Nidever, D. L., Olsen, K., Blum, R. D., Besla, G., Zaritsky, D., van, d., Bell, E. F., Gallart, C., Cioni, M. L., Johnson, L. C., Katherina, V. A., Saha, A., de, B., Noel, N., Monachesi, A., Massana, P., Conn, B. C., Martinez-Delgado, D., , Munoz, R. R., et al. (2018). SMASHing the LMC: A Tidally Induced Warp in the Outer LMC and a Large-scale Reddening Map. ASTROPHYSICAL JOURNAL, 866(2).
• DeMaio, T., Gonzalez, A. H., Zabludoff, A., Zaritsky, D., Connor, T., Donahue, M., & Mulchaey, J. S. (2018). Lost but not forgotten: intracluster light in galaxy groups and clusters. MNRAS, 474(3), 3009-3031.
• DeMaio, T., Gonzalez, A., Zabludoff, A., Zaritsky, D., Connor, T., Donahue, M., & Mulchaey, J. (2018). Lost but not forgotten: intracluster light in galaxy groups and clusters. MNRAS, 474, 3009-3031.
• Deger, S., Rudnick, G., Kelkar, K., Aragon-Salamanca, A., Desai, V., Lotz, J. M., Jablonka, P., Moustakas, J., & Zaritsky, D. (2018). Tidal Interactions and Mergers in Intermediate-redshift EDisCS Clusters. ASTROPHYSICAL JOURNAL, 869(1).
• Finn, R. A., Desai, V., Rudnick, G., Balogh, M., Haynes, M. P., Jablonka, P., Koopmann, R. A., Moustakas, J., Peng, C. Y., Poggianti, B., Rines, K., & Zaritsky, D. (2018). The Local Cluster Survey. I. Evidence of Outside-in Quenching in Dense Environments. ASTROPHYSICAL JOURNAL, 862(2).
• Kadowaki, J., Zhang, H., Zaritsky, D., Donnerstein, R. L., Dey, A., Zhang, H., Zaritsky, D., Spekkens, K., Rahman, M., Martinez-delgado, D., Karunakaran, A., Kadowaki, J., Donnerstein, R. L., & Dey, A. (2018). Systematically Measuring Ultra-diffuse Galaxies (SMUDGes). I. Survey Description and First Results in the Coma Galaxy Cluster and Environs. Astrophysical Journal Supplement Series, 240(1), 1. doi:10.3847/1538-4365/aaefe9
  More info

  We present a homogeneous catalog of 275 large (effective radius $\gtrsim$ 5.3 arcsec) ultra-diffuse galaxy (UDG) candidates lying within an $\approx$ 290 square degree region surrounding the Coma cluster. The catalog results from our automated postprocessing of data from the Legacy Surveys, a three-band imaging survey covering 14,000 square degrees of the extragalactic sky. We describe a pipeline that identifies UDGs and provides their basic parameters. The survey is as complete in these large UDGs as previously published UDG surveys of the central region of the Coma cluster. We conclude that the majority of our detections are at roughly the distance of the Coma cluster, implying effective radii $\ge 2.5$ kpc, and that our sample contains a significant number of analogs of DF 44, where the effective radius exceeds 4 kpc, both within the cluster and in the surrounding field. The $g-z$ color of our UDGs spans a large range, suggesting that even large UDGs may reflect a range of formation histories. A majority of the UDGs are consistent with being lower stellar mass analogs of red sequence galaxies, but we find both red and blue UDG candidates in the vicinity of the Coma cluster and a relative overabundance of blue UDG candidates in the lower density environments and the field. Our eventual processing of the full Legacy Surveys data will produce the largest, most homogeneous sample of large UDGs.
• Kingsley, J. S., Angel, R., Davison, W., Neff, D., Teran, J., Assenmacher, B., Peyton, K., Martin, H. M., Oh, C., Kim, D., Pearce, E., Rascon, M., Connors, T., Alfred, D., Jannuzi, B. T., Zaritsky, D., Christensen, E., Males, J., Hinz, P., , Seaman, R., et al. (2018). An inexpensive turnkey 6.5-m observatory with customizing options. GROUND-BASED AND AIRBORNE TELESCOPES VII, 10700.
• Mutlu-Pakdil, B., Sand, D. J., Carlin, J. L., Spekkens, K., Caldwell, N., Crnojevic, D., Hughes, A. K., Willman, B., & Zaritsky, D. (2018). A Deeper Look at the New Milky Way Satellites: Sagittarius II, Reticulum II, Phoenix II, and Tucana III. ASTROPHYSICAL JOURNAL, 863(1).
• Sivanandam, S., Moon, D., Meyer, R. E., Grunhut, J., Zaritsky, D., Eisner, J., Ma, K. e., Henderson, C., Blank, B., Chou, C., Jarvis, M. E., Eikenberry, S., Chun, M., & Park, B. (2018). The Wide Integral Field Infrared Spectrograph: Commissioning Results and On-sky Performance. GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY VII, 10702.
• Weiner, B. J., Sand, D., Gabor, P., Johnson, C., Swindell, S., Kubanek, P., Gasho, V., Golota, T., Jannuzi, B., Milne, P., Smith, N., & Zaritsky, D. (2018). Development of the Arizona Robotic Telescope Network. OBSERVATORY OPERATIONS: STRATEGIES, PROCESSES, AND SYSTEMS VII, 10704.
• Zaritsky, D. F. (2018). Development of the Arizona Robotic Telescope Network. Proc. SPIE.
  More info

  The Arizona Robotic Telescope Network (ARTN) project is a long term effort todevelop a system of telescopes to carry out a flexible program of PI observing,survey projects, and time domain astrophysics including monitoring, rapidresponse, and transient/target-of-opportunity followup. Steward Observatoryoperates and shares in several 1-3m class telescopes with quality sites andinstrumentation, largely operated in classical modes. Science programs suitedto these telescopes are limited by scheduling flexibility and people-power ofavailable observers. Our goal is to adapt these facilities for multipleco-existing queued programs, interrupt capability, remote/robotic operation,and delivery of reduced data. In the long term, planning for the LSST era, weenvision an automated system coordinating across multiple telescopes and sites,where alerts can trigger followup, classification, and triggering of furtherobservations if required, such as followup imaging that can triggerspectroscopy. We are updating telescope control systems and software toimplement this system in stages, beginning with the Kuiper 61'' and VaticanObservatory 1.8-m telescopes. The Kuiper 61'' and its Mont4K camera can now becontrolled and queue-scheduled by the RTS2 observatory control software, andoperated from a remote room at Steward. We discuss science and technicalrequirements for ARTN, and some of the challenges in adapting heterogenouslegacy facilities, scheduling, data pipelines, and maintaining capabilities fora diverse user base.[Journal_ref: Proc. SPIE 10704, 107042H (10 July 2018)]
• Zaritsky, D. F. (2018). The Wide Integral Field Infrared Spectrograph: Commissioning Results and On-sky Performance. Proc. SPIE.
  More info

  We have recently commissioned a novel infrared ($0.9-1.7$ $\mu$m) integralfield spectrograph (IFS) called the Wide Integral Field Infrared Spectrograph(WIFIS). WIFIS is a unique instrument that offers a very large field-of-view(50$^{\prime\prime}$ x 20$^{\prime\prime}$) on the 2.3-meter Bok telescope atKitt Peak, USA for seeing-limited observations at moderate spectral resolvingpower. The measured spatial sampling scale is $\sim1\times1^{\prime\prime}$ andits spectral resolving power is $R\sim2,500$ and $3,000$ in the $zJ$($0.9-1.35$ $\mu$m) and $H_{short}$ ($1.5-1.7$ $\mu$m) modes, respectively.WIFIS's corresponding etendue is larger than existing near-infrared (NIR)IFSes, which are mostly designed to work with adaptive optics systems andtherefore have very narrow fields. For this reason, this instrument isspecifically suited for studying very extended objects in the near-infraredsuch as supernovae remnants, galactic star forming regions, and nearbygalaxies, which are not easily accessible by other NIR IFSes. This enablesscientific programs that were not originally possible, such as detailed surveysof a large number of nearby galaxies or a full accounting of nucleosyntheticyields of Milky Way supernova remnants. WIFIS is also designed to be easilyadaptable to be used with larger telescopes. In this paper, we report on theoverall performance characteristics of the instrument, which were measuredduring our commissioning runs in the second half of 2017. We presentmeasurements of spectral resolving power, image quality, instrumentalbackground, and overall efficiency and sensitivity of WIFIS and compare themwith our design expectations. Finally, we present a few example observationsthat demonstrate WIFIS's full capability to carry out infrared imagingspectroscopy of extended objects, which is enabled by our custom data reductionpipeline.[Journal_ref: ]
• Zhang, H., Zaritsky, D., & Behroozi, P. (2018). Emission from the Ionized Gaseous Halos of Low-redshift Galaxies and Their Neighbors. ASTROPHYSICAL JOURNAL, 861(1).
• Zhang, H., Zaritsky, D., Werk, J., & Behroozi, P. (2018). Emission Line Ratios for the Circumgalactic Medium and the "Bimodal" Nature of Galaxies. ASTROPHYSICAL JOURNAL LETTERS, 866(1).
• Balogh, M. L., Gilbank, D. G., Muzzin, A., Rudnick, G., Cooper, M. C., Lidman, C., Biviano, A., Demarco, R., McGee, S. L., Nantais, J. B., Noble, A., Old, L., Wilson, G., Yee, H., Bellhouse, C., Cerulo, P., Chan, J., Pintos-Castro, I., Simpson, R., , van, d., et al. (2017). Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: survey description. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 470(4), 4168-4185.
• Balogh, M., Gilbank, D., Muzzin, A., Rudnick, G., Cooper, M., Lidman, C., Biviano, A., Demarco, R., McGee, S., Nantais, J., Noble, A., Old, L., Wilson, G., Yee, H., Bellhouse, C., Cerulo, P., Chan, J., Pintos-Castro, I. .., Simpson, R., , Burg, R., et al. (2017). "Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: survey description". mnras, 470, 4168-4185.
• Bennet, P., Sand, D. J., Crnojevic, D., Spekkens, K., Zaritsky, D., & Karunakaran, A. (2017). Discovery of Diffuse Dwarf Galaxy Candidates around M101. ASTROPHYSICAL JOURNAL, 850(1).
• Bennet, P., Sand, D., Crnojevi{'c}, D., Spekkens, K., Zaritsky, D., & Karunakaran, A. (2017). "Discovery of Diffuse Dwarf Galaxy Candidates around M101". apj, 850, 109.
• Bitsakis, T., Bonfini, P., Gonzalez-Lopezlira, R. A., Ramirez-Siordia, V. H., Bruzual, G., Charlot, S., Maravelias, G., & Zaritsky, D. (2017). A Novel Method to Automatically Detect and Measure the Ages of Star Clusters in Nearby Galaxies: Application to the Large Magellanic Cloud. ASTROPHYSICAL JOURNAL, 845(1).
• Bitsakis, T., Bonfini, P., Gonz{'alez-L'opezlira}, R., Ram{'{i}rez-Siordia}, V., Bruzual, G., Charlot, S., Maravelias, G., & Zaritsky, D. (2017). "A Novel Method to Automatically Detect and Measure the Ages of Star Clusters in Nearby Galaxies: Application to the Large Magellanic Cloud". apj, 845, 56.
• DeMaio, T., Gonzalez, A. H., Zabludoff, A., & Zaritsky, D. (2017). On the origin of the intracluster light in massive galaxy clusters (vol 472, pg 2543, 2017). MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 472(3), 2543-+.
• Kadowaki, J., Zaritsky, D., & Donnerstein, R. (2017). "Spectroscopy of Ultra-diffuse Galaxies in the Coma Cluster". apjl, 838, L21.
• Kadowaki, J., Zaritsky, D., & Donnerstein, R. L. (2017). Spectroscopy of Ultra-diffuse Galaxies in the Coma Cluster. ASTROPHYSICAL JOURNAL LETTERS, 838(2).
• Nidever, D. L., Olsen, K., Walker, A. R., Katherina, V. A., Blum, R. D., Kaleida, C., Choi, Y., Conn, B. C., Gruendl, R. A., Bell, E. F., Besla, G., Munoz, R. R., Gallart, C., Martin, N. F., Olszewski, E. W., Saha, A., Monachesi, A., Monelli, M., de, B., , Johnson, L. C., et al. (2017). SMASH: Survey of the MAgellanic Stellar History. ASTRONOMICAL JOURNAL, 154(5).
• Nidever, D., Olsen, K., Walker, A., Vivas, A., Blum, R., Kaleida, C., Choi, Y., Conn, B., Gruendl, R., Bell, E., Besla, G., Mu{~noz}, R., Gallart, C., Martin, N., Olszewski, E., Saha, A., Monachesi, A., Monelli, M., Boer, T., , Johnson, L., et al. (2017). "SMASH: Survey of the MAgellanic Stellar History". aj, 154, 199.
• Park, H. S., Moon, D., Zaritsky, D., Pak, M., Lee, J., Kim, S. C., Kim, D., & Cha, S. (2017). Dwarf Galaxy Discoveries from the KMTNet Supernova Program. I. The NGC 2784 Galaxy Group. ASTROPHYSICAL JOURNAL, 848(1).
• Park, H., Moon, D., Zaritsky, D., Pak, M., Lee, J., Kim, S., Kim, D., & Cha, S. (2017). "Dwarf Galaxy Discoveries from the KMTNet Supernova Program. I. The NGC 2784 Galaxy Group". apj, 848, 19.
• Rudnick, G., Jablonka, P., Moustakas, J., Aragon-Salamanca, A., Zaritsky, D., Jaffe, Y. L., De, L. G., Desai, V., Halliday, C., Just, D., Milvang-Jensen, B., & Poggianti, B. (2017). Determining the Halo Mass Scale Where Galaxies Lose Their Gas. ASTROPHYSICAL JOURNAL, 850(2).
• Rudnick, G., Jablonka, P., Moustakas, J., Arag{'on-Salamanca}, A., Zaritsky, D., Jaff{'e}, Y., De Lucia, G., Desai, V., Halliday, C., Just, D., Milvang-Jensen, B. .., & Poggianti, B. (2017). "Determining the Halo Mass Scale Where Galaxies Lose Their Gas". apj, 850, 181.
• Zaritsky, D. (2017). "Clues to the nature of ultradiffuse galaxies from estimated galaxy velocity dispersions". mnras, 464, L110-L113.
• Zaritsky, D. F. (2017). Clues to the nature of ultradiffuse galaxies from estimated galaxy velocity dispersions. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 464(1), L110-L113.
• Zaritsky, D., & Courtois, H. (2017). "A dynamics-free lower bound on the mass of our Galaxy". mnras, 465, 3724-3728.
• Zaritsky, D., & Courtois, H. (2017). A dynamics-free lower bound on the mass of our Galaxy. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 465(3), 3724-3728.
• Zhang, H., & Zaritsky, D. (2017). "The Galaxy's veil of excited hydrogen". Nature Astronomy, 1, 0103.
• Zhang, H., & Zaritsky, D. (2017). The Galaxy's veil of excited hydrogen. NATURE ASTRONOMY, 1(5).
• Cantale, N., Jablonka, P., Courbin, F., Rudnick, G., Zaritsky, D., Meylan, G., Desai, V., De, L. G., Aragon-Salamanca, A., Poggianti, B. M., Finn, R., & Simard, L. (2016). Disc colours in field and cluster spiral galaxies at 0.5 less than or similar to z less than or similar to 0.8. ASTRONOMY & ASTROPHYSICS, 589.
• De, M. G., Panagia, N., Sabbi, E., Lennon, D., Anderson, J., van, d., Cignoni, M., Grebel, E. K., Larsen, S., Zaritsky, D., Zeidler, P., Gouliermis, D., & Aloisi, A. (2016). Hubble Tarantula Treasury Project - IV. The extinction law(star). MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 455(4), 4373-4387.
• Gallagher, J. S., Zeidler, P., Zaritsky, D., Tosi, M., Smith, L. J., Sana, H., Sabbi, E., Ryon, J. E., Panagia, N., Mink, S. E., Marel, R. P., Marchi, G. D., Lennon, D. J., Larsen, S. S., Koekemoer, A. M., Iii, J. S., Grebel, E. K., Gouliermis, D. A., Gordon, K. D., , Gallagher, J. S., et al. (2016). HUBBLE TARANTULA TREASURY PROJECT. III. PHOTOMETRIC CATALOG AND RESULTING CONSTRAINTS ON THE PROGRESSION OF STAR FORMATION IN THE 30 DORADUS REGION. Astrophysical Journal Supplement Series, 222(1), 11. doi:10.3847/0067-0049/222/1/11
  More info

  We present and describe the astro-photometric catalog of more than 800,000 sources found in the Hubble Tarantula Treasury Project (HTTP). HTTP is a Hubble Space Telescope Treasury program designed to image the entire 30 Doradus region down to the sub-solar (~0.5 M⊙) mass regime using the Wide Field Camera 3 and the Advanced Camera for Surveys. We observed 30 Doradus in the near-ultraviolet (F275W, F336W), optical (F555W, F658N, F775W), and near-infrared (F110W, F160W) wavelengths. The stellar photometry was measured using point-spread function fitting across all bands simultaneously. The relative astrometric accuracy of the catalog is 0.4 mas. The astro-photometric catalog, results from artificial star experiments, and the mosaics for all the filters are available for download. Color–magnitude diagrams are presented showing the spatial distributions and ages of stars within 30 Dor as well as in the surrounding fields. HTTP provides the first rich and statistically significant sample of intermediate- and low-mass pre-main sequence candidates and allows us to trace how star formation has been developing through the region. The depth and high spatial resolution of our analysis highlight the dual role of stellar feedback in quenching and triggering star formation on the giant H ii region scale. Our results are consistent with stellar sub-clustering in a partially filled gaseous nebula that is offset toward our side of the Large Magellanic Cloud.
• Jannuzi, B. T., Zaritsky, D., Zaritsky, D., Watson, A. M., Vargas, M. L., Uribe, J. A., Urdaibay, D., Teran, J. U., Sierra, G., Sanchez, B., Richer, M. G., Reyes-ruiz, M., Perez-calpena, A., Pedrayes, M. H., Ortega, F. R., Norton, T. J., Lee, W. H., Jannuzi, B. T., Hill, D. L., , Herrera, J., et al. (2016). The Telescopio San Pedro Mártir project. Proceedings of SPIE, 9906. doi:10.1117/12.2232000
  More info

  The Telescopio San Pedro Martir project intends to construct a 6.5m telescope to be installed at the Observatorio Astronomico Nacional in the Sierra San Pedro Martir in northern Baja California, Mexico. The project is an association of Mexican institutions, lead by the Instituto Nacional de Astrofisica, Optica y Electronica and the Instituto de Astronomia at the Universidad Nacional Autonoma de Mexico, in partnership with the Smithsonian Astrophysical Observatory and the University of Arizona’s Department of Astronomy and Steward Observatory. The project is currently in the planning and design stage. Once completed, the partners plan to operate the MMT and TSPM as a binational astrophysical observatory.
• Martin, N. F., Jungbluth, V., Nidever, D. L., Bell, E. F., Besla, G., Blum, R. D., Cioni, M. L., Conn, B. C., Kaleida, C. C., Gallart, C., Jin, S., Majewski, S. R., Martinez-Delgado, D., Monachesi, A., Munoz, R. R., Noel, N., Olsen, K., Stringfellow, G. S., van, d., , Vivas, A. K., et al. (2016). SMASH 1: A VERY FAINT GLOBULAR CLUSTER DISRUPTING IN THE OUTER REACHES OF THE LMC?. ASTROPHYSICAL JOURNAL LETTERS, 830(1).
• Zaritsky, D., Crnojevic, D., & Sand, D. J. (2016). ARE SOME MILKY WAY GLOBULAR CLUSTERS HOSTED BY UNDISCOVERED GALAXIES?. ASTROPHYSICAL JOURNAL LETTERS, 826(1).
• Zaritsky, D., Mayo, L., & Gabor, P. (2016). Education and public engagement in observatory operations. Proceedings of SPIE, 9910. doi:10.1117/12.2234465
  More info

  Education and public engagement (EPE) is an essential part of astronomy’s mission. New technologies, remote observing and robotic facilities are opening new possibilities for EPE. A number of projects (e.g., Telescopes In Education, MicroObservatory, Goldstone Apple Valley Radio Telescope and UNC’s Skynet) have developed new infrastructure, a number of observatories (e.g., University of Arizona’s “full-engagement initiative” towards its astronomy majors, Vatican Observatory’s collaboration with high-schools) have dedicated their resources to practical instruction and EPE. Some of the facilities are purpose built, others are legacy telescopes upgraded for remote or automated observing. Networking among institutions is most beneficial for EPE, and its implementation ranges from informal agreements between colleagues to advanced software packages with web interfaces. The deliverables range from reduced data to time and hands-on instruction while operating a telescope. EPE represents a set of tasks and challenges which is distinct from research applications of the new astronomical facilities and operation modes. In this paper we examine the experience with several EPE projects, and some lessons and challenges for observatory operation.
• Zaritsky, D., McCabe, K., Aravena, M., Athanassoula, E., Bosma, A., Comeron, S., Courtois, H. M., Elmegreen, B. G., Elmegreen, D. M., Erroz-Ferrer, S., Gadotti, D. A., Hinz, J. L., Ho, L. C., Holwerda, B., Kim, T., Knapen, J. H., Laine, J., Laurikainen, E., Carlos, M. J., , Salo, H., et al. (2016). GLOBULAR CLUSTER POPULATIONS: RESULTS INCLUDING S(4)G LATE-TYPE GALAXIES. ASTROPHYSICAL JOURNAL, 818(1).
• Zhang, H., Zaritsky, D., Zhu, G., Menard, B., & Hogg, D. W. (2016). HYDROGEN EMISSION FROM THE IONIZED GASEOUS HALOS OF LOW-REDSHIFT GALAXIES. ASTROPHYSICAL JOURNAL, 833(2).
• {Cantale}, N., {Jablonka}, P., {Courbin}, F., {Rudnick}, G., {Zaritsky}, D., {Meylan}, G., {Desai}, V., {De Lucia}, G., {Arag{\'o}n-Salamanca}, A., {Poggianti}, B., {Finn}, R., , L. (2016). Disc colours in field and cluster spiral galaxies at 0.5 {\lsim}z {\lsim} 0.8. Astronomy & Astrophysics, 589, A82.
• {Crnojevi{\'c}}, D., {Sand}, D., {Zaritsky}, D., {Spekkens}, K., {Willman}, B., , J. (2016). Deep Imaging of Eridanus II and Its Lone Star Cluster. Astrophysical Journal Letters, 824, L14.
• {De Marchi}, G., {Panagia}, N., {Sabbi}, E., {Lennon}, D., {Anderson}, J., Marel}, R., {Cignoni}, M., {Grebel}, E., {Larsen}, S., {Zaritsky}, D., {Zeidler}, P., {Gouliermis}, D., , A. (2016). Hubble Tarantula Treasury Project - IV. The extinction law. MNRAS, 455, 4373-4387.
• {Fong}, W., {Margutti}, R., {Chornock}, R., {Berger}, E., {Shappee}, B., {Levan}, A., {Tanvir}, N., {Smith}, N., {Milne}, P., {Laskar}, T., {Fox}, D., {Lunnan}, R., {Blanchard}, P., {Hjorth}, J., {Wiersema}, K., Horst}, A., , D. (2016). The Afterglow and Early-type Host Galaxy of the Short GRB 150101B at z = 0.1343. Astrophysical Journal, 833, 151.
• {Martin}, N., {Jungbluth}, V., {Nidever}, D., {Bell}, E., {Besla}, G., {Blum}, R., {Cioni}, M., {Conn}, B., {Kaleida}, C., {Gallart}, C., {Jin}, S., {Majewski}, S., {Martinez-Delgado}, D., {Monachesi}, A., {Mu{\~n}oz}, R., {No{\"e}l}, N., {Olsen}, K., {Stringfellow}, G., Marel}, R., , {Vivas}, A., et al. (2016). SMASH 1: A Very Faint Globular Cluster Disrupting in the Outer Reaches of the LMC?. Astrophysical Journal Letters, 830, L10.
• {Sabbi}, E., {Lennon}, D., {Anderson}, J., {Cignoni}, M., Marel}, R., {Zaritsky}, D., {De Marchi}, G., {Panagia}, N., {Gouliermis}, D., {Grebel}, E., {Gallagher}, J., {Smith}, L., {Sana}, H., {Aloisi}, A., {Tosi}, M., {Evans}, C., {Arab}, H., {Boyer}, M., {de Mink}, S., , {Gordon}, K., et al. (2016). Hubble Tarantula Treasury Project. III. Photometric Catalog and Resulting Constraints on the Progression of Star Formation in the 30 Doradus Region. Astrophysical Journal Supplements, 222, 11.
• {Zaritsky}, D. (2016). A Universal Kinematic Scaling Relation and Galaxy Bulges. Galactic Bulges, 418, 185.
• {Zaritsky}, D., {McCabe}, K., {Aravena}, M., {Athanassoula}, E., {Bosma}, A., {Comer{\'o}n}, S., {Courtois}, H., {Elmegreen}, B., {Elmegreen}, D., {Erroz-Ferrer}, S., {Gadotti}, D., {Hinz}, J., {Ho}, L., {Holwerda}, B., {Kim}, T., {Knapen}, J., {Laine}, J., {Laurikainen}, E., {Mu{\~n}oz-Mateos}, J., , {Salo}, H., et al. (2016). Globular Cluster Populations: Results Including S$^{4}$G Late-type Galaxies. Astrophysical Journal, 818, 99.
• {Zhang}, H., , D. (2016). Examining early-type galaxy scaling relations using simple dynamical models. MNRAS, 455, 1364-1374.
• {Zhang}, H., {Zaritsky}, D., {Zhu}, G., {M{\'e}nard}, B., , D. (2016). Hydrogen Emission from the Ionized Gaseous Halos of Low-redshift Galaxies. Astrophysical Journal, 833, 276.
• Bouquin, A. Y., de Paz, A. G., Boissier, S., Munoz-Mateos, J., Sheth, K., Zaritsky, D., Laine, J., Gallego, J., Peletier, R. F., Roeck, B. R., & Knapen, J. H. (2015). THE GALEX/S(4)G UV-IR COLOR-COLOR DIAGRAM: CATCHING SPIRAL GALAXIES AWAY FROM THE BLUE SEQUENCE. ASTROPHYSICAL JOURNAL LETTERS, 800(1).
• Buta, R. J., Sheth, K., Athanassoula, E., Bosma, A., Knapen, J. H., Laurikainen, E., Salo, H., Elmegreen, D., Ho, L. C., Zaritsky, D., Courtois, H., Hinz, J. L., Munoz-Mateos, J., Kim, T., Regan, M. W., Gadotti, D. A., de Paz, A. G., Laine, J., Menendez-Delmestre, K., , Comeron, S., et al. (2015). A CLASSICAL MORPHOLOGICAL ANALYSIS OF GALAXIES IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G). ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 217(2).
• Carlos Munoz-Mateos, J., Sheth, K., Regan, M., Kim, T., Laine, J., Erroz-Ferrer, S., Gil de Paz, A., Comeron, S., Hinz, J., Laurikainen, E., Salo, H., Athanassoula, E., Bosma, A., Bouquin, A. Y., Schinnerer, E., Ho, L., Zaritsky, D., Gadotti, D. A., Madore, B., , Holwerda, B., et al. (2015). THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G): STELLAR MASSES, SIZES, AND RADIAL PROFILES FOR 2352 NEARBY GALAXIES. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 219(1).
• DeMaio, T., Gonzalez, A. H., Zabludoff, A., Zaritsky, D., & Bradac, M. (2015). On the origin of the intracluster light in massive galaxy clusters. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 448(2), 1162-1177.
• Hinz, J. L., Zaritsky, D., Sheth, K., Salo, H., Regan, M. W., Querejeta, M., Paz, A. G., Munoz-mateos, J. C., Mizusawa, T., Menendez-delmestre, K., Meidt, S. E., Laurikainen, E., Laine, S., Laine, J., Knapen, J. H., Kim, T., Ho, L. C., Hinz, J. L., Gadotti, D. A., , Erroz-ferrer, S., et al. (2015). The spitzer survey of stellar structure in galaxies (S^4G): multi-component decomposition strategies and data release. Astrophysical Journal Supplement Series, 219(1), 4. doi:10.1088/0067-0049/219/1/4
  More info

  The Spitzer Survey of Stellar Structure in Galaxies (S^4G) is a deep 3.6 and 4.5 μm imaging survey of 2352 nearby (
• Kelkar, K., Aragon-Salamanca, A., Gray, M. E., Maltby, D., Vulcani, B., De Lucia, G., Poggianti, B. M., & Zaritsky, D. (2015). Galaxy sizes as a function of environment at intermediate redshift from the ESO Distant Cluster Survey. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 450(2), 1246-1255.
• Kim, T., Sheth, K., Gadotti, D. A., Lee, M. G., Zaritsky, D., Elmegreen, B. G., Athanassoula, E., Bosma, A., Holwerda, B., Ho, L. C., Comeron, S., Knapen, J. H., Hinz, J. L., Munoz-Mateos, J., Erroz-Ferrer, S., Buta, R. J., Kim, M., Laurikainen, E., Salo, H., , Madore, B. F., et al. (2015). THE MASS PROFILE AND SHAPE OF BARS IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G): SEARCH FOR AN AGE INDICATOR FOR BARS. ASTROPHYSICAL JOURNAL, 799(1).
• Martin, N. F., Nidever, D. L., Besla, G., Olsen, K., Walker, A. R., Vivas, A. K., Gruendl, R. A., Kaleida, C. C., Munoz, R. R., Blum, R. D., Saha, A., Conn, B. C., Bell, E. F., Chu, Y., Cioni, M. L., de Boer, T. J., Gallart, C., Jin, S., Kunder, A., , Majewski, S. R., et al. (2015). HYDRA II: A FAINT AND COMPACT MILKY WAY DWARF GALAXY FOUND IN THE SURVEY OF THE MAGELLANIC STELLAR HISTORY. ASTROPHYSICAL JOURNAL LETTERS, 804(1).
• Nidever, D. L., Besla, G., Olszewski, E. W., Zaritsky, D., Zaritsky, D., Walker, A. R., Vivas, A. K., Stringfellow, G. S., Saha, A., Olszewski, E. W., Olsen, K., Noel, N. E., Nidever, D. L., Munoz, R. R., Monteagudo, L., Monelli, M., Monachesi, A., Martinez-delgado, D., Martin, N. F., , Marel, R. P., et al. (2015). Hydra II: a faint and compact milky way dwarf galaxy found in the survey of the magellanic stellar history. The Astrophysical Journal, 804(1), L5. doi:10.1088/2041-8205/804/1/l5
  More info

  © 2015. The American Astronomical Society. All rights reserved.We present the discovery of a new dwarf galaxy, Hydra II, found serendipitously within the data from the ongoing Survey of the Magellanic Stellar History conducted with the Dark Energy Camera on the Blanco 4 m Telescope. The new satellite is compact (r h = 68 ± 11 pc) and faint (M V = -4.8 ± 0.3), but well within the realm of dwarf galaxies. The stellar distribution of Hydra II in the color-magnitude diagram is well-described by a metal-poor ([Fe/H] = -2.2) and old (13 Gyr) isochrone and shows a distinct blue horizontal branch, some possible red clump stars, and faint stars that are suggestive of blue stragglers. At a heliocentric distance of 134 ± 10 kpc, Hydra II is located in a region of the Galactic halo that models have suggested may host material from the leading arm of the Magellanic Stream. A comparison with N-body simulations hints that the new dwarf galaxy could be or could have been a satellite of the Magellanic Clouds.
• Querejeta, M., Meidt, S. E., Schinnerer, E., Cisternas, M., Carlos Munoz-Mateos, J., Sheth, K., Knapen, J., Van de Ven, G., Norris, M. A., Peletier, R., Laurikainen, E., Salo, H., Holwerda, B. W., Athanassoula, E., Bosma, A., Groves, B., Ho, L. C., Gadotti, D. A., Zaritsky, D., , Regan, M., et al. (2015). THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G): PRECISE STELLAR MASS DISTRIBUTIONS FROM AUTOMATED DUST CORRECTION AT 3.6 mu m. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 219(1).
• Salo, H., Laurikainen, E., Laine, J., Comeron, S., Gadotti, D. A., Buta, R., Sheth, K., Zaritsky, D., Ho, L., Knapen, J., Athanassoula, E., Bosma, A., Laine, S., Cisternas, M., Kim, T., Munoz-Mateos, J. C., Regan, M., Hinz, J. L., Gil de Paz, A., , Menendez-Delmestre, K., et al. (2015). THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G): MULTI-COMPONENT DECOMPOSITION STRATEGIES AND DATA RELEASE. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 219(1).
• Treu, T., Zaritsky, D., Zaritsky, D., Treu, T., Sharon, K., Schrabback, T., Schmidt, K. B., Ryan, R. E., Lubin, L. M., Linden, A. V., Lemaux, B. C., Jr, R. E., Huang, K. H., Hoag, A., Hinz, J. L., Hildebrandt, H., Gonzalez, A. H., Cain, B., & Bradac, M. (2015). RCS2 J232727.6-020437: AN EFFICIENT COSMIC TELESCOPE AT z = 0.6986. The Astrophysical Journal, 813(1), 37. doi:10.1088/0004-637x/813/1/37
  More info

  Here, we present a detailed gravitational lens model of the galaxy cluster RCS2 J232727.6-020437. Due to cosmological dimming of cluster members and ICL, its high redshift (z=0.6986) makes it ideal for studying background galaxies. Using new ACS and WFC3/IR HST data, we identify 16 multiple images. From MOSFIRE follow up, we identify a strong emission line in the spectrum of one multiple image, likely confirming the redshift of that system to z=2.083. With a highly magnified (μ ≳ 2) source plane area of ~ 0.7 arcmin2 at z = 7, RCS2 J232727.6-020437 has a lensing efficiency comparable to the Hubble Frontier Fields clusters. We discover four highly magnified z ~ 7 candidate Lyman-break galaxies behind the cluster, one of which may be multiply-imaged. Correcting for magnification, we find that all four galaxies are fainter than 0.5L*. One candidate is detected at >10σ in both Spitzer/IRAC [3.6] and [4.5] channels. A spectroscopic follow-up with MOSFIRE does not result in the detection of the Lyman-alpha emission line from any of the four candidates. From the MOSFIRE spectra we place median upper limits on the Lyman-alpha flux of 5 – 14 × 10–19 ergs–1cm–2 (5σ).
• Zaritsky, D. F. (2015). Confirmation of Hostless Type IA Supernovae Using Hubble Space Telescope Images. ApJ, 807, 83.
• Zaritsky, D. F. (2015). Giant disk galaxies: Where environment trumps mass in galaxy evolution. MNRAS, 448, 1767.
• Zaritsky, D. F. (2015). Hubbel Tarantula Treasury Project. II. Optical and Near Infrared Star Formation History of the Starburst Region NGC 2070 in 30 Doradus. ApJ, 811, 76.
• Zaritsky, D. F. (2015). RCS2 J232727.6-020437: An Efficient Cosmic Telescope at z = 0.6986. ApJ, 813, 37.
• Zaritsky, D. F. (2015). The Odd Offset Between the Galactic Disk and Its Bar in NGC 3906. ApJ, 808, 90.
• Zaritsky, D. F. (2015). The connection between the UV colour of early type galaxies and the stellar initial mass fucntion revisited. MNRAS, 446, 2030.
• Zaritsky, D., Aravena, M., Athanassoula, E., Bosma, A., Comeron, S., Elmegreen, B. G., Erroz-Ferrer, S., Gadotti, D. A., Hinz, J. L., Ho, L. C., Holwerda, B., Knapen, J. H., Laine, J., Laurikainen, E., Carlos Munoz-Mateos, J., Salo, H., & Sheth, K. (2015). GLOBULAR CLUSTER POPULATIONS: FIRST RESULTS FROM S(4)G EARLY-TYPE GALAXIES. ASTROPHYSICAL JOURNAL, 799(2).
• Zaritsky, D., Halford, M., Zaritsky, D., & Halford, M. (2015). The bottom-light present day mass function of the peculiar globular cluster NGC 6535. The Astrophysical Journal, 815(2), 86. doi:10.1088/0004-637x/815/2/86
  More info

  Dynamical mass calculations have suggested that the Milky Way globular cluster NGC 6535 belongs to a population of clusters with high mass-to-light ratios, possibly due to a bottom-heavy stellar initial mass function (IMF). We use published Hubble Space Telescope data to measure the present day stellar mass function of this cluster within its half-light radius and instead find that it is bottom-light, exacerbating the discrepancy between the dynamical measurement and its known stellar content. The cluster's proximity to the Milky Way bulge and its relatively strong velocity anisotropy are both reasons to be suspicious of the dynamical mass measurement, but we find that neither straightforwardly explains the sense and magnitude of the discrepancy. Although there are alternative potential explanations for the high mass-to-light ratio, such as the presence of large numbers of stellar remnants or dark matter, we find this cluster to be sufficiently perplexing that we now exclude it from a discussion of possible variations in the IMF. Because this was the sole known old, Milky Way cluster in the population of high dynamical mass-to-light ratio clusters, some possible explanations for the difference in cluster properties are again open for consideration.
• Zaritsky, D., Holwerda, B. W., Zaritsky, D., Sheth, K., Seibert, M., Salo, H., Regan, M. W., Paz, A. G., Munoz-mateos, J. C., Mizusawa, T., Menendez-delmestre, K., Madore, B. F., Laurikainen, E., Laine, J., Knapen, J. H., Kim, T., Holwerda, B. W., Ho, L. C., Hinz, J. L., , Gadotti, D. A., et al. (2015). A Classical Morphological Analysis of Galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G). Astrophysical Journal Supplement Series, 217(2), 32. doi:10.1088/0067-0049/217/2/32
  More info

  The Spitzer Survey of Stellar Structure in Galaxies (S(4)G) is the largest available database of deep, homogeneous middle-infrared (mid-IR) images of galaxies of all types. The survey, which includes 2352 nearby galaxies, reveals galaxy morphology only minimally affected by interstellar extinction. This paper presents an atlas and classifications of S(4)G galaxies in the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system. The CVRHS system follows the precepts of classical de Vaucouleurs morphology, modified to include recognition of other features such as inner, outer, and nuclear lenses, nuclear rings, bars, and disks, spheroidal galaxies, X patterns and box/peanut structures, OLR subclass outer rings and pseudorings, bar ansae and barlenses, parallel sequence latetypes, thick disks, and embedded disks in 3D early-type systems. We show that our CVRHS classifications are internally consistent, and that nearly half of the S(4)G sample consists of extreme late-type systems (mostly bulgeless, pure disk galaxies) in the range Scd-Im. The most common family classification for mid-IR types S0/a to Sc is SA while that for types Scd to Sm is SB. The bars in these two type domains are very different in mid-IR structure and morphology. This paper examines the bar, ring, and type classification fractions in the sample, and also includes several montages of images highlighting the various kinds of "stellar structures" seen in mid-IR galaxy morphology.
• Zaritsky, D., Holwerda, B. W., Zaritsky, D., Ven, G. V., Sheth, K., Seibert, M., Schinnerer, E., Salo, H., Regan, M. W., Querejeta, M., Peletier, R., Paz, A. G., Norris, M. A., Munoz-mateos, J. C., Mizusawa, T., Menendez-delmestre, K., Meidt, S. E., Laurikainen, E., Laine, J., , Knapen, J. H., et al. (2015). The Spitzer Survey of Stellar Structure in Galaxies (S4G): Precise Stellar Mass Distributions from Automated Dust Correction at 3.6 μm. Astrophysical Journal Supplement Series, 219(1), 5. doi:10.1088/0067-0049/219/1/5
  More info

  The mid-infrared is an optimal window to trace stellar mass in nearby galaxies and the 3.6μm IRAC band has been exploited to this effect, but such mass estimates can be biased by dust emission. We present our pipeline to reveal the old stellar flux at 3.6 μm and obtain stellar mass maps for more than 1600 galaxies available from the Spitzer Survey of Stellar Structure in Galaxies (S^4G). This survey consists of images in two infrared bands (3.6 and 4.5μm), and we use the Independent Component Analysis (ICA) method presented in Meidt et al. to separate the dominant light from old stars and the dust emission that can significantly contribute to the observed 3.6μm flux. We exclude from our ICA analysis galaxies with low signal-to-noise ratio (S/N
• Zaritsky, D., Sand, D. J., Pritchet, C. J., & Graham, M. L. (2015). CONFIRMATION OF HOSTLESS TYPE Ia SUPERNOVAE USING HUBBLE SPACE TELESCOPE IMAGING. The Astrophysical Journal, 807(1), 83. doi:10.1088/0004-637x/807/1/83
  More info

  We present deep Hubble Space Telescope imaging at the locations of four, potentially hostless, long-faded Type Ia supernovae (SNe Ia) in low-redshift, rich galaxy clusters that were identified in the Multi-Epoch Nearby Cluster Survey. Assuming a steep faint-end slope for the galaxy cluster luminosity function (), our data include?all but ?of the stellar mass in cluster galaxies ( with ), a factor of 10 better than our ground-based imaging. Two of the four SNe Ia still have no possible host galaxy associated with them (), confirming that their progenitors belong to the intracluster (IC) stellar population. The third SN Ia appears near a faint disk galaxy (), which has a relatively high probability of being a chance alignment. A faint, red?point source coincident with the fourth SN Ia?s explosion position () may be either a globular cluster (GC) or a faint dwarf galaxy. We estimate the local surface densities of GCs and dwarfs to show that a GC is more likely, due to the proximity of an elliptical galaxy, but neither can be ruled out. This faint host implies that the SN Ia rate in dwarfs or GCs may be enhanced, but remains within previous observational constraints. We demonstrate that our results do not preclude the use of SNe Ia as bright tracers of IC light at higher redshifts, but that it will be necessary to first refine the constraints on their rate in dwarfs and GCs with deep imaging for a larger sample of low-redshift, apparently hostless SNe Ia.
• Zeidler, P., Zaritsky, D., Tosi, M., Smith, L. J., Sabbi, E., Marel, R. P., Marchi, G. D., Lennon, D. J., Grebel, E. K., Gouliermis, D. A., Cignoni, M., Anderson, J., & Aloisi, A. (2015). HUBBLE TARANTULA TREASURY PROJECT. II. THE STAR-FORMATION HISTORY OF THE STARBURST REGION NGC 2070 IN 30 DORADUS. The Astrophysical Journal, 811(2), 76. doi:10.1088/0004-637x/811/2/76
• de, S. B., Sheth, K., Kim, T., Pardy, S., D', O. E., Wilcots, E., Hinz, J., Munoz-Mateos, J., Regan, M. W., Athanassoula, E., Bosma, A., Buta, R. J., Cisternas, M., Comeron, S., Gadotti, D. A., Gil, d., Jarrett, T. H., Elmegreen, B. G., Erroz-Ferrer, S., , Ho, L. C., et al. (2015). THE ODD OFFSET BETWEEN THE GALACTIC DISK AND ITS BAR IN NGC 3906. ASTROPHYSICAL JOURNAL, 808(1).
• Bradac, M., Ryan, R., Casertano, S., Huang, K., Lemaux, B. C., Schrabback, T., Gonzalez, A. H., Allen, S., Cain, B., Gladders, M., Hall, N., Hildebrandt, H., Hinz, J., von, d., Lubin, L., Treu, T., & Zaritsky, D. (2014). SPITZER ULTRA FAINT SURVEY PROGRAM (SURFS UP). I. AN OVERVIEW. ASTROPHYSICAL JOURNAL, 785(2).
• Bradač, M., Ryan, R., Casertano, S., Huang, K., Lemaux, B. C., Schrabback, T., Gonzalez, A. H., Allen, S., Cain, B., Gladders, M., Hall, N., Hildebrandt, H., Hinz, J., Von, A., Lubin, L., Treu, T., & Zaritsky, D. (2014). Spitzer ultra faint survey program (SURFS UP). I. an overview. Astrophysical Journal, 785(2).
  More info

  Abstract: Spitzer UltRa Faint SUrvey Program is a joint Spitzer and Hubble Space Telescope Exploration Science program using 10 galaxy clusters as cosmic telescopes to study z ≳ 7 galaxies at intrinsically lower luminosities, enabled by gravitational lensing, than blank field surveys of the same exposure time. Our main goal is to measure stellar masses and ages of these galaxies, which are the most likely sources of the ionizing photons that drive reionization. Accurate knowledge of the star formation density and star formation history at this epoch is necessary to determine whether these galaxies indeed reionized the universe. Determination of the stellar masses and ages requires measuring rest-frame optical light, which only Spitzer can probe for sources at z ≳ 7, for a large enough sample of typical galaxies. Our program consists of 550 hr of Spitzer/IRAC imaging covering 10 galaxy clusters with very well-known mass distributions, making them extremely precise cosmic telescopes. We combine our data with archival observations to obtain mosaics with 30 hr exposure time in both 3.6 μm and 4.5 μm in the central 4′ × 4′ field and 15 hr in the flanking fields. This results in 3σ sensitivity limits of 26.6 and 26.2 AB magnitudes for the central field in the IRAC 3.6 and 4.5 μm bands, respectively. To illustrate the survey strategy and characteristics we introduce the sample, present the details of the data reduction and demonstrate that these data are sufficient for in-depth studies of z ≳ 7 sources (using a z = 9.5 galaxy behind MACS J1149.5+2223 as an example). For the first cluster of the survey (the Bullet Cluster) we have released all high-level data mosaics and IRAC empirical point-spread function models. In the future we plan to release these data products for the entire survey. © 2014. The American Astronomical Society. All rights reserved.
• Graham, M., Sand, D., Valenti, S., Howell, D., Parrent, J., Halford, M., Zaritsky, D. F., Blanco, F., Rest, A., & Dilday, B. (2014). Clues to the Nature fo SN 2009ip from Photometric and Spectroscopic Evolution to Late Times. Astrophysical Journal, 787, 163.
• Guennou, L., Adami, C., Durret, F., Neto, G. L., Ulmer, M. P., Clowe, D., Lebrun, V., Martinet, N., Allam, S., Annis, J., Basa, S., Benoist, C., Biviano, A., Cappi, A., Cypriano, E. S., Gavazzi, R., Halliday, C., Ilbert, O., Jullo, E., , Just, D., et al. (2014). Structure and substructure analysis of DAFT/FADA galaxy clusters in the [0.4-0.9] redshift range. Astronomy and Astrophysics, 561.
  More info

  Abstract: Context. The DAFT/FADA survey is based on the study of ~90 rich (masses found in the literature >2 × 1014 M ⊙) and moderately distant clusters (redshifts 0.4 < z < 0.9), all with HST imaging data available. This survey has two main objectives: to constrain dark energy (DE) using weak lensing tomography on galaxy clusters and to build a database (deep multi-band imaging allowing photometric redshift estimates, spectroscopic data, X-ray data) of rich distant clusters to study their properties. Aims. We analyse the structures of all the clusters in the DAFT/FADA survey for which XMM-Newton and/or a sufficient number of galaxy redshifts in the cluster range are available, with the aim of detecting substructures and evidence for merging events. These properties are discussed in the framework of standard cold dark matter (ΛCDM) cosmology. Methods. In X-rays, we analysed the XMM-Newton data available, fit a β-model, and subtracted it to identify residuals. We used Chandra data, when available, to identify point sources. In the optical, we applied a Serna & Gerbal (SG) analysis to clusters with at least 15 spectroscopic galaxy redshifts available in the cluster range. We discuss the substructure detection efficiencies of both methods. Results. XMM-Newton data were available for 32 clusters, for which we derive the X-ray luminosity and a global X-ray temperature for 25 of them. For 23 clusters we were able to fit the X-ray emissivity with a β-model and subtract it to detect substructures in the X-ray gas. A dynamical analysis based on the SG method was applied to the clusters having at least 15 spectroscopic galaxy redshifts in the cluster range: 18 X-ray clusters and 11 clusters with no X-ray data. The choice of a minimum number of 15 redshifts implies that only major substructures will be detected. Ten substructures were detected both in X-rays and by the SG method. Most of the substructures detected both in X-rays and with the SG method are probably at their first cluster pericentre approach and are relatively recent infalls. We also find hints of a decreasing X-ray gas density profile core radius with redshift. Conclusions. The percentage of mass included in substructures was found to be roughly constant with redshift values of 5-15%, in agreement both with the general CDM framework and with the results of numerical simulations. Galaxies in substructures show the same general behaviour as regular cluster galaxies; however, in substructures, there is a deficiency of both late type and old stellar population galaxies. Late type galaxies with recent bursts of star formation seem to be missing in the substructures close to the bottom of the host cluster potential well. However, our sample would need to be increased to allow a more robust analysis. © 2014 ESO.
• Guennou, L., Biviano, A., Adami, C., Limousin, M., Lima Neto, G., Mamon, G., Ulmer, M., Gavazzi, R., Cypriano, E., Durret, F., Clowe, D., LeBrun, V., Allam, S., Basa, S., Benoist, C., Cappi, A., Halliday, C., Ilbert, O., Johnston, D., , Jullo, E., et al. (2014). Mass profile and dynamical status of the z ~ 0.8 galaxy cluster LCDCS 0504. Astronomy & Astrophysics, 566, 149.
• Holwerda, B. W., Muñoz-Mateos, J., Comerón, S., Meidt, S., Sheth, K., Laine, S., Hinz, J. L., Regan, M. W., Gil, A., Menéndez-Delmestre, K., Seibert, M., Kim, T., Mizusawa, T., Laurikainen, E., Salo, H., Laine, J., Gadotti, D. A., Zaritsky, D., Erroz-Ferrer, S., , Ho, L. C., et al. (2014). Morphological parameters of a spitzer survey of stellar structure in galaxies. Astrophysical Journal, 781(1).
  More info

  Abstract: The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), asymmetry (A), smoothness (S), the Gini index (G), the relative contribution of the brightest pixels to the second-order moment of the flux (M20), ellipticity (E), and the Gini index of the second-order moment (GM) have all been applied to morphologically classify galaxies at various wavelengths. Here, we present a catalog of these parameters for the Spitzer Survey of stellar structure in Galaxies, a volume-limited, near-infrared (NIR) imaging survey of nearby galaxies using the 3.6 and 4.5 μm channels of the Infrared Array Camera on board the Spitzer Space Telescope. Our goal is to provide a reference catalog of NIR quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, non-interacting galaxies-those typically found on the Hubble tuning fork-lie in this parameter space and show that there is a tight relation between concentration (C82) and M20 for normal galaxies. M 20 can be used to classify galaxies into earlier and later types (i.e., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer NIR imaging. We find that four relations, based on the parameters A and S, G and M20, GM, C, and M20, respectively, select outliers in morphological parameter space, but each selects different subsets of galaxies. Two criteria (GM > 0.6, G >-0.115 × M20 + 0.384) seem most appropriate to identify possible mergers and the merger fraction in NIR surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on concentration and M20. © 2014. The American Astronomical Society. All rights reserved.
• Jaffe, Y. L., Aragon-Salamanca, A., Ziegler, B., Kuntschner, H., Zaritsky, D., Rudnick, G., Poggianti, B. M., Hoyos, C., Halliday, C., & Demarco, R. (2014). Ionized gas discs in elliptical and S0 galaxies at z < 1. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 440(4), 3491-3502.
• Jaffe, Y., Aragon-Salamanca, A., Ziegler, B., Kuntschner, H., Zaritsky, D. F., Rudnick, G., Poggianti, B., Hoyos, C., Halliday, C., Demarco, R., Jaffe, Y., Aragon-Salamanca, A., Ziegler, B., Kuntschner, H., Zaritsky, D. F., Rudnick, G., Poggianti, B., Hoyos, C., Halliday, C., & Demarco, R. (2014). Ionized gas discs in elliptical and S0 galaxies at z < 1. Monthly Notices of the Royal Astronomical Society, 440, 3491.
• Kim, T., Gadotti, D. A., Sheth, K., Athanassoula, E., Bosma, A., Lee, M. G., Madore, B. F., Elmegreen, B., Knapen, J. H., Zaritsky, D., Ho, L. C., Comeron, S., Holwerda, B., Hinz, J. L., Munoz-Mateos, J., Cisternas, M., Erroz-Ferrer, S., Buta, R., Laurikainen, E., , Salo, H., et al. (2014). UNVEILING THE STRUCTURE OF BARRED GALAXIES AT 3.6 mu m WITH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G). I. DISK BREAKS. ASTROPHYSICAL JOURNAL, 782(2).
• Kim, T., Gadotti, D. A., Sheth, K., Athanassoula, E., Bosma, A., Lee, M. G., Madore, B. F., Elmegreen, B., Knapen, J. H., Zaritsky, D., Ho, L. C., Comerón, S., Holwerda, B., Hinz, J. L., Muñoz-Mateos, J., Cisternas, M., Erroz-Ferrer, S., Buta, R., Laurikainen, E., , Salo, H., et al. (2014). Unveiling the structure of barred galaxies at 3.6 mu;m with the spitzer survey of stellar structure in galaxies (S⁴G). I. Disk breaks. Astrophysical Journal, 782(2).
  More info

  Abstract: We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T ≥ 0.1, the break radius to bar radius, r bar, varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r bar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds. © 2014. The American Astronomical Society. All rights reserved. © 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
• Laine, J., Laurikainen, E., Salo, H., Comeron, S., Buta, R., Zaritsky, D. F., Athanassoula, E., Bosma, A., Munoz-Mateos, J., Gadotti, D., Hinz, J., Erroz-Ferrer, S., Gil de Paz, A., Kim, T., Menendez-Delmestre, K., Mizusawa, T., Regan, M., Seibert, M., & Sheth, K. (2014). Morphology and environment of galaxies with disc breaks in the S4G and NIRS0S. Monthly Notices of the Royal Astronomical Society, 441, 1992.
• Laine, S., Knapen, J. H., Munoz-Mateos, J., Kim, T., Comeron, S., Martig, M., Holwerda, B. W., Athanassoula, E., Bosma, A., Johansson, P. H., Erroz-Ferrer, S., Gadotti, D. A., de, P., Hinz, J., Laine, J., Laurikainen, E., Menendez-Delmestre, K., Mizusawa, T., Regan, M. W., , Salo, H., et al. (2014). Spitzer/Infrared Array Camera near-infrared features in the outer parts of S(4)G galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 444(4), 3015-3039.
• Laine, S., Knapen, J., Munoz-Mateos, J., Kim, T., Comeron, S., Martig, M., Holwerda, B., Athanassoula, E., Bosma, A., Johansson, P., Erroz-Ferrer, S., Gadotti, D., Gil de Paz, A., Hinz, J., Laine, J., Laurikainen, E., Menendez-Delmestre, K., Mizusawa, T., Regan, M., , Salo, H., et al. (2014). Spitzer/Infrared Array Camera near infrared features in the outer parts of S4G galaxies. Monthly Notices of the Royal Astronomical Society, 444, 3015.
• Meidt, S. E., Schinnerer, E., van, d., Zaritsky, D., Peletier, R., Knapen, J. H., Sheth, K., Regan, M., Querejeta, M., Munoz-Mateos, J., Kim, T., Hinz, J. L., de, P., Athanassoula, E., Bosma, A., Buta, R. J., Cisternas, M., Ho, L. C., Holwerda, B., , Skibba, R., et al. (2014). RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S(4)G IRAC 3.6 AND 4.5 mu m IMAGES. II. THE CONVERSION FROM LIGHT TO MASS. ASTROPHYSICAL JOURNAL, 788(2).
• Ryan, R., Gonzalez, A., Lemaux, B., Bradac, M., Casertano, S., Allen, S., Cain, B., Gladders, M., Hall, N., Hildebradt, H., Hinz, J., Huang, K., Lubin, L., Schrabback, T., Stiavelli, M., Treu, T., von der Linden, A., & Zaritsky, D. F. (2014). Measuring the Stellar Masses of z ~ 7 Galaxies with the Spitzer Ultrafaint Survey Program (SURFS UP). Astrophyiscal Journal Letters, 786, L4.
• Schinnerer, E., van de Ven, G., Peletier, R., Zaritsky, D. F., Knapen, J., Sheth, K., Regan, M., Querejeta, M., Munoz-Mateos, J., Kim, T., Hinz, J., Gil de Paz, A., Athanassoula, E., Bosma, A., Buta, R., Cisternas, M., Ho, L., Holweda, B., Skibba, R., , Laurikainen, E., et al. (2014). Reconstructing the Stellar Mass Distribution of Galaxies Using S4G IRAC 3.6 and 4.5 micron Images. II. The Conversion from Light to Mass. Astrophysical Journal, 788, 144.
• Zaritsky, D. F., Colucci, J., Pessev, P., Bernstein, R., & Chandar, R. (2014). Evidence for Two Distinct Stellar Initial Mass Functions: Probing for Clues to the Dichotomy. Astrophysical Journal, 796, 71.
• Zaritsky, D. F., Courtois, H., Munoz-Mateos, J., Sorce, J., Erroz-Ferrer, S., Comeron, S., Gadotti, D., Gil de Paz, A., Hinz, J., Laurikainen, E., Kim, T., Laine, J., Menendez-Delmestre, K., Mizusawa, T., Regan, M., Salo, H., Seibert, M., Sheth, K., Athanassoula, E., , Bosma, A., et al. (2014). The Baryonic Tully-Fisher Relationship for S4G Galaxies and the "Condensed" Baryon Fraction of Galaxies. Astronomical Journal, 147, 134.
• Zaritsky, D., Colucci, J. E., Pessev, P. M., Bernstein, R. A., & Chandar, R. (2014). EVIDENCE FOR TWO DISTINCT STELLAR INITIAL MASS FUNCTIONS: PROBING FOR CLUES TO THE DICHOTOMY. ASTROPHYSICAL JOURNAL, 796(2).
• Zaritsky, D., Courtois, H., Munoz-Mateos, J., Sorce, J., Erroz-Ferrer, S., Comeron, S., Gadotti, D. A., Gil, D., Hinz, J. L., Laurikainen, E., Kim, T., Laine, J., Menendez-Delmestre, K., Mizusawa, T., Regan, M. W., Salo, H., Seibert, M., Sheth, K., Athanassoula, E., , Bosma, A., et al. (2014). THE BARYONIC TULLY-FISHER RELATIONSHIP FOR S(4)G GALAXIES AND THE "CONDENSED" BARYON FRACTION OF GALAXIES. ASTRONOMICAL JOURNAL, 147(6).
• Zaritsky, D., Gil, A., & Y., A. (2014). An empirical connection between the ultraviolet color of early-type galaxies and the stellar initial mass function. Astrophysical Journal Letters, 780(1).
  More info

  Abstract: Using new UV magnitudes for a sample of early-type galaxies (ETGs) with published stellar mass-to-light ratios, Υ*, we find a correlation between UV color and Υ* that is tighter than those previously identified between Υ* and either the central stellar velocity dispersion, metallicity, or alpha enhancement. The sense of the correlation is that galaxies with larger Υ* are bluer in the UV. We conjecture that differences in the lower mass end of the stellar initial mass function (IMF) are related to the nature of the extreme horizontal branch populations that are generally responsible for the UV flux in ETGs. If so, then UV color can be used to identify ETGs with particular IMF properties and to estimate Υ*. © 2014. The American Astronomical Society. All rights reserved.
• Zaritsky, D., Gil, d., & Bouquin, A. (2014). AN EMPIRICAL CONNECTION BETWEEN THE ULTRAVIOLET COLOR OF EARLY-TYPE GALAXIES AND THE STELLAR INITIAL MASS FUNCTION. ASTROPHYSICAL JOURNAL LETTERS, 780(1).
• Zaritsky, D., Treu, T., Hall, N., Zaritsky, D., Treu, T., Stiavelli, M., Schrabback, T., Ryan, R. E., Lubin, L. M., Linden, A. V., Lemaux, B. C., Huang, K. H., Hinz, J., Hildebradt, H., Hall, N. R., Gonzalez, A. H., Gladders, M. D., Casertano, S., Cain, B., , Bradac, M., et al. (2014). MEASURING THE STELLAR MASSES OF z ∼ 7 GALAXIES WITH THE SPITZER ULTRAFAINT SURVEY PROGRAM (SURFS UP)*. The Astrophysical Journal, 786(1), L4. doi:10.1088/2041-8205/786/1/l4
  More info

  We present Spitzer/IRAC observations of nine z'-band dropouts highly magnified (2 ≲ μ ≲ 12) by the Bullet Cluster. We combine archival imaging with our Exploratory program (SURFS UP), which results in a total integration time of ∼30 hr per Infrared Array Camera (IRAC) band. We detect (≳ 3σ) in both IRAC bands the brightest of these high-redshift galaxies, with [3.6] = 23.80 ± 0.28 mag, [4.5] = 23.78 ± 0.25 mag, and (H – [3.6]) = 1.17 ± 0.32 mag. The remaining eight galaxies are undetected to [3.6] ∼ 26.4 mag and [4.5] ∼ 26.0 mag with stellar masses of ∼5 × 10{sup 7} M {sub ☉}. The detected galaxy has an estimated magnification of μ = 12 ± 4, which implies this galaxy has an ultraviolet luminosity of L{sub 1500}∼0.3 L{sub z=7}{sup ∗}—the lowest-luminosity individual source detected in IRAC at z ≳ 7. By modeling the broadband photometry, we estimate the galaxy has an intrinsic star formation rate (SFR) of SFR ∼ 1.3 M {sub ☉} yr{sup –1} and stellar mass of M ∼ 2.0 × 10{sup 9} M {sub ☉}, which gives a specific star formation rate of sSFR ∼ 0.7 Gyr{sup –1}. If this galaxy had sustained this SFR since z ∼more » 20, it could have formed the observed stellar mass (to within a factor of ∼2). We also discuss alternate star formation histories and argue that the exponentially increasing model is unlikely. Finally, based on the intrinsic SFR, we estimate that this galaxy has a likely [C II] flux of (f {sub [C} {sub II]}) = 1.6 mJy.« less
• Cisternas, M., Gadotti, D. A., Knapen, J. H., Kim, T., Diaz-Garcia, S., Laurikainen, E., Salo, H., Gonzalez-Martin, O., Ho, L. C., Elmegreen, B. G., Zaritsky, D., Sheth, K., Athanassoula, E., Bosma, A., Comeron, S., Erroz-Ferrer, S., Gil, D., Hinz, J. L., Holwerda, B. W., , Laine, J., et al. (2013). X-RAY NUCLEAR ACTIVITY IN S(4)G BARRED GALAXIES: NO LINK BETWEEN BAR STRENGTH AND CO-OCCURRENT SUPERMASSIVE BLACK HOLE FUELING. ASTROPHYSICAL JOURNAL, 776(1).
• Cisternas, M., Gadotti, D. A., Knapen, J. H., Kim, T., Díaz-García, S., Laurikainen, E., Salo, H., González-Martín, O., Ho, L. C., Elmegreen, B. G., Zaritsky, D., Sheth, K., Athanassoula, E., Bosma, A., Comerón, S., Erroz-Ferrer, S., Gil, A., Hinz, J. L., Holwerda, B. W., , Laine, J., et al. (2013). X-ray nuclear activity in s⁴g barred galaxies: No link between bar strength and co-occurrent supermassive black hole fueling. Astrophysical Journal, 776(1).
  More info

  Abstract: Stellar bars can lead to gas inflow toward the center of a galaxy and stimulate nuclear star formation. However, there is no compelling evidence on whether they also feed a central supermassive black hole: by measuring the fractions of barred active and inactive galaxies, previous studies have yielded conflicting results. In this paper, we aim to understand the lack of observational evidence for bar-driven active galactic nucleus (AGN) activity by studying a sample of 41 nearby (d < 35 Mpc) barred galaxies from the Spitzer Survey for Stellar Structure in Galaxies. We use Chandra observations to measure nuclear 2-10 keV X-ray luminosities and estimate Eddington ratios, together with Spitzer 3.6 μm imaging to quantify the strength of the stellar bar in two independent ways: (1) from its structure, as traced by its ellipticity and boxiness, and (2) from its gravitational torque Qb , taken as the maximum ratio of the tangential force to the mean background radial force. In this way, rather than discretizing the presence of both stellar bars and nuclear activity, we are able to account for the continuum of bar strengths and degrees of AGN activity. We find nuclear X-ray sources in 31 out of 41 galaxies with median X-ray luminosity and Eddington ratio of L X = 4.3 × 1038 erg s-1 and L bol/L Edd = 6.9 × 10-6, respectively, consistent with low-luminosity AGN activity. Including upper limits for those galaxies without nuclear detections, we find no significant correlation between any of the bar strength indicators and the degree of nuclear activity, irrespective of galaxy luminosity, stellar mass, Hubble type, or bulge size. Strong bars do not favor brighter or more efficient nuclear activity, implying that at least for the low-luminosity regime, supermassive black hole fueling is not closely connected to large-scale features. © 2013. The American Astronomical Society. All rights reserved.
• Gonzalez, A. H., Sivanandam, S., Zabludoff, A. I., & Zaritsky, D. (2013). GALAXY CLUSTER BARYON FRACTIONS REVISITED. ASTROPHYSICAL JOURNAL, 778(1).
• Holwerda, B. W., Zaritsky, D., Zaritsky, D., Sheth, K., Seibert, M., Salo, H., Regan, M. W., Pirzkal, N., Paz, A. G., Munoz-mateos, J. C., Mizusawa, T., Menendez-delmestre, K., Meidt, S. E., Laurikainen, E., Laine, S., Laine, J., Knapen, J. H., Kim, T., Holwerda, B. W., , Ho, L. C., et al. (2013). Morphological parameters of a Spitzer survey of stellar structure in galaxies. The Astrophysical Journal, 781(1), 12. doi:10.1088/0004-637x/781/1/12
  More info

  The morphology of galaxies can be quantified to some degree using a set of scale-invariant parameters. Concentration (C), asymmetry (A), smoothness (S), the Gini index (G), the relative contribution of the brightest pixels to the second-order moment of the flux (M-20), ellipticity (E), and the Gini index of the second-order moment (G(M)) have all been applied to morphologically classify galaxies at various wavelengths. Here, we present a catalog of these parameters for the Spitzer Survey of stellar structure in Galaxies, a volume-limited, near-infrared (NIR) imaging survey of nearby galaxies using the 3.6 and 4.5 mu m channels of the Infrared Array Camera on board the Spitzer Space Telescope. Our goal is to provide a reference catalog of NIR quantified morphology for high-redshift studies and galaxy evolution models with enough detail to resolve stellar mass morphology. We explore where normal, non-interacting galaxies-those typically found on the Hubble tuning fork-lie in this parameter space and show that there is a tight relation between concentration (C-82) and M-20 for normal galaxies. M-20 can be used to classify galaxies into earlier and later types (i.e., to separate spirals from irregulars). Several criteria using these parameters exist to select systems with a disturbed morphology, i.e., those that appear to be undergoing a tidal interaction. We examine the applicability of these criteria to Spitzer NIR imaging. We find that four relations, based on the parameters A and S, G and M-20, G(M), C, and M-20, respectively, select outliers in morphological parameter space, but each selects different subsets of galaxies. Two criteria (G(M) \textgreater 0.6, G \textgreater -0.115 x M-20 + 0.384) seem most appropriate to identify possible mergers and the merger fraction in NIR surveys. We find no strong relation between lopsidedness and most of these morphological parameters, except for a weak dependence of lopsidedness on concentration and M-20.
• Munoz-Mateos, J. C., Sheth, K., de, P., Meidt, S., Athanassoula, E., Bosma, A., Comeron, S., Elmegreen, D. M., Elmegreen, B. G., Erroz-Ferrer, S., Gadotti, D. A., Hinz, J. L., Ho, L. C., Holwerda, B., Jarrett, T. H., Kim, T., Knapen, J. H., Laine, J., Laurikainen, E., , Madore, B. F., et al. (2013). THE IMPACT OF BARS ON DISK BREAKS AS PROBED BY S(4)G IMAGING. ASTROPHYSICAL JOURNAL, 771(1).
• Muñoz-Mateos, J. C., Sheth, K., Gil, A., Meidt, S., Athanassoula, E., Bosma, A., Comerón, S., Elmegreen, D. M., Elmegreen, B. G., Erroz-Ferrer, S., Gadotti, D. A., Hinz, J. L., Ho, L. C., Holwerda, B., Jarrett, T. H., Kim, T., Knapen, J. H., Laine, J., Laurikainen, E., , Madore, B. F., et al. (2013). The impact of bars on disk breaks as probed by S⁴G imaging. Astrophysical Journal, 771(1).
  More info

  Abstract: We have analyzed the radial distribution of old stars in a sample of 218 nearby face-on disks, using deep 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. In particular, we have studied the structural properties of those disks with a broken or down-bending profile. We find that, on average, disks with a genuine single-exponential profile have a scale length and a central surface brightness which are intermediate to those of the inner and outer components of a down-bending disk with the same total stellar mass. In the particular case of barred galaxies, the ratio between the break and the bar radii (R br/R bar) depends strongly on the total stellar mass of the galaxy. For galaxies more massive than 1010 M ⊙, the distribution is bimodal, peaking at R br/R bar ∼ 2 and ∼3.5. The first peak, which is the most populated one, is linked to the outer Lindblad resonance of the bar, whereas the second one is consistent with a dynamical coupling between the bar and the spiral pattern. For galaxies below 1010 M⊙, breaks are found up to ∼10 R bar, but we show that they could still be caused by resonances given the rising nature of rotation curves in these low-mass disks. While not ruling out star formation thresholds, our results imply that radial stellar migration induced by non-axisymmetric features can be responsible not only for those breaks at ∼2 R bar, but also for many of those found at larger radii. © 2013. The American Astronomical Society. All rights reserved.
• Sabbi, E., Anderson, J., Lennon, D. J., Van, R., Aloisi, A., Boyer, M. L., Cignoni, M., Marchi, G. D., Mink, S. D., Evans, C. J., Gallagher, J. S., Gordon, K., Gouliermis, D. A., Grebel, E. K., Koekemoer, A. M., Larsen, S. S., Panagia, N., Ryon, J. E., Smith, L. J., , Tosi, M., et al. (2013). Hubble tarantula treasury project: Unraveling Tarantula's web. I. Observational overview and first results. Astronomical Journal, 146(3).
  More info

  Abstract: The Hubble Tarantula Treasury Project (HTTP) is an ongoing panchromatic imaging survey of stellar populations in the Tarantula Nebula in the Large Magellanic Cloud that reaches into the sub-solar mass regime (
• Sanderson, A., O'Sullivan, E., Ponman, T. J., Gonzalez, A. H., Sivanandam, S., Zabludoff, A. I., & Zaritsky, D. (2013). The baryon budget on the galaxy group/cluster boundary. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 429(4), 3288-3304.
• Zaritsky, D., Colucci, J. E., Pessev, P. M., Bernstein, R. A., & Chandar, R. (2013). EVIDENCE FOR TWO DISTINCT STELLAR INITIAL MASS FUNCTIONS: REVISITING THE EFFECTS OF CLUSTER DYNAMICAL EVOLUTION. ASTROPHYSICAL JOURNAL, 770(2).
• Zaritsky, D., Colucci, J. E., Pessev, P. M., Bernstein, R. A., & Chandar, R. (2013). Evidence for two distinct stellar initial mass functions: Revisiting the effects of cluster dynamical evolution. Astrophysical Journal, 770(2).
  More info

  Abstract: We measure the velocity dispersions of six galactic globular clusters using spatially integrated spectra, to test for the effects of internal dynamical evolution in the stellar mass-to-light ratios, Υ*, of star clusters. In particular, we revisit whether the low values of Υ* that we found in our previous study, from which we concluded that there are at least two population of stellar clusters with distinct stellar initial mass functions, are artificially depressed by relaxation driven mass loss. The combination of our previous sample of five old clusters and these six now provide an order of magnitude range in cluster mass with which to explore this issue. We find no relationship between cluster mass, or relaxation time, and Υ*. Because relaxation is mass dependent, we conclude that the values of Υ* for these clusters are not strongly affected by dynamical effects, and so confirm the presence of the population of clusters with low Υ*. © 2013. The American Astronomical Society. All rights reserved..
• Zaritsky, D., Paz, A. G., & Bouquin, A. Y. (2013). AN EMPIRICAL CONNECTION BETWEEN THE ULTRAVIOLET COLOR OF EARLY-TYPE GALAXIES AND THE STELLAR INITIAL MASS FUNCTION. The Astrophysical Journal, 780(1), L1. doi:10.1088/2041-8205/780/1/l1
  More info

  Using new UV magnitudes for a sample of early-type galaxies (ETGs) with published stellar mass-to-light ratios, Υ_*, we find a correlation between UV color and Υ_* that is tighter than those previously identified between Υ_* and either the central stellar velocity dispersion, metallicity, or alpha enhancement. The sense of the correlation is that galaxies with larger Υ_* are bluer in the UV. We conjecture that differences in the lower mass end of the stellar initial mass function (IMF) are related to the nature of the extreme horizontal branch populations that are generally responsible for the UV flux in ETGs. If so, then UV color can be used to identify ETGs with particular IMF properties and to estimate Υ_*.
• Zaritsky, D., Salo, H., Laurikainen, E., Elmegreen, D., Athanassoula, E., Bosma, A., Comeron, S., Erroz-Ferrer, S., Elmegreen, B., Gadotti, D. A., de, P., Hinz, J. L., Ho, L. C., Holwerda, B. W., Kim, T., Knapen, J. H., Laine, J., Laine, S., Madore, B. F., , Meidt, S., et al. (2013). ON THE ORIGIN OF LOPSIDEDNESS IN GALAXIES AS DETERMINED FROM THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G). ASTROPHYSICAL JOURNAL, 772(2).
• Zaritsky, D., Salo, H., Laurikainen, E., Elmegreen, D., Athanassoula, E., Bosma, A., Comerón, S., Erroz-Ferrer, S., Elmegreen, B., Gadotti, D. A., Gil, A., Hinz, J. L., Ho, L. C., Holwerda, B. W., Kim, T., Knapen, J. H., Laine, J., Laine, S., Madore, B. F., , Meidt, S., et al. (2013). On the origin of lopsidedness in galaxies as determined from the spitzer survey of stellar structure in galaxies (S⁴G). Astrophysical Journal, 772(2).
  More info

  Abstract: We study the m = 1 distortions (lopsidedness) in the stellar components of 167 nearby galaxies that span a wide range of morphologies and luminosities. We confirm the previous findings of (1) a high incidence of lopsidedness in the stellar distributions, (2) increasing lopsidedness as a function of radius out to at least 3.5 exponential scale lengths, and (3) greater lopsidedness, over these radii, for galaxies of later type and lower surface brightness. Additionally, the magnitude of the lopsidedness (1) correlates with the character of the spiral arms (stronger arm patterns occur in galaxies with less lopsidedness), (2) is not correlated with the presence or absence of a bar, or the strength of the bar when one is present, (3) is inversely correlated to the stellar mass fraction, f*, within one radial scale length, and (4) correlates directly with f* measured within the radial range over which we measure lopsidedness. We interpret these findings to mean that lopsidedness is a generic feature of galaxies and does not, generally, depend on a rare event, such as a direct accretion of a satellite galaxy onto the disk of the parent galaxy. While lopsidedness may be caused by several phenomena, moderate lopsidedness (〈A1〉i + 〈A 1〉o )/2 < 0.3) is likely to reflect halo asymmetries to which the disk responds or a gravitationally self-generated mode. We hypothesize that the magnitude of the stellar response depends both on how centrally concentrated the stars are with respect to the dark matter and whether there are enough stars in the region of the lopsidedness that self-gravity is dynamically important. © 2013. The American Astronomical Society. All rights reserved.
• Adams, S. M., Zaritsky, D., Sand, D. J., Graham, M. L., Bildfell, C., Hoekstra, H., & Pritchet, C. (2012). THE ENVIRONMENTAL DEPENDENCE OF THE INCIDENCE OF GALACTIC TIDAL FEATURES. ASTRONOMICAL JOURNAL, 144(5).
• Adams, S. M., Zaritsky, D., Sand, D. J., Graham, M. L., Bildfell, C., Hoekstra, H., & Pritchet, C. (2012). The environmental dependence of the incidence of galactic tidal features. Astronomical Journal, 144(5).
  More info

  Abstract: In a sample of 54 galaxy clusters (0.04 < z < 0.15) containing 3551 early-type galaxies suitable for study, we identify those with tidal features both interactively and automatically. We find that 3% have tidal features that can be detected with data that reach a 3σ sensitivity limit of 26.5 mag arcsec -2. Regardless of the method used to classify tidal features, or the fidelity imposed on such classifications, we find a deficit of tidally disturbed galaxies with decreasing clustercentric radius that is most pronounced inside of ∼0.5 R 200. We cannot distinguish whether the trend arises from an increasing likelihood of recent mergers with increasing clustercentric radius or a decrease in the lifetime of tidal features with decreasing clustercentric radius. We find no evidence for a relationship between local density and the incidence of tidal features, but our local density measure has large uncertainties. We find interesting behavior in the rate of tidal features among cluster early-types as a function of clustercentric radius and expect such results to provide constraints on the effect of the cluster environment on the structure of galaxy halos, the build-up of the red sequence of galaxies, and the origin of the intracluster stellar population. © © 2012. The American Astronomical Society. All rights reserved..
• Bildfell, C., Hoekstra, H., Babul, A., Sand, D., Graham, M., Willis, J., Urquhart, S., Mahdavi, A., Pritchet, C., Zaritsky, D., Franse, J., & Langelaan, P. (2012). Evolution of the red sequence giant to dwarf ratio in galaxy clusters out to z ∼ 0.5. Monthly Notices of the Royal Astronomical Society, 425(1), 204-221.
  More info

  Abstract: We analyse deep g′ and r′ band data of 97 galaxy clusters imaged with MegaCam on the Canada-France-Hawaii telescope. We compute the number of luminous (giant) and faint (dwarf) galaxies using criteria based on the definitions of de Lucia et al. Due to excellent image quality and uniformity of the data and analysis, we probe the giant-to-dwarf ratio (GDR) out to z ∼ 0.55. With X-ray temperature (T x) information for the majority of our clusters, we constrain, for the first time, the T x-corrected giant and dwarf evolution separately. Our measurements support an evolving GDR over the redshift range 0.05 ≤ z ≤ 0.55. We show that modifying the (g′ - r′), mr′ and K-correction used to define dwarf and giant selection does not alter the conclusion regarding the presence of evolution. We parametrize the GDR evolution using a linear function of redshift (GDR =αz+β) with a best-fitting slope of α = 0.88 ± 0.15 and normalization β = 0.44 ± 0.03. Contrary to claims of a large intrinsic scatter, we find that the GDR data can be fully accounted for using observational errors alone. Consistently, we find no evidence for a correlation between GDR and cluster mass (via T x or weak lensing). Finally, the data suggest that the evolution of the GDR at z < 0.2 is driven primarily by dry merging of the massive giant galaxies, which when considered with previous results at higher redshift, suggests a change in the dominant mechanism that mediates the GDR. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
• Boyer, M. L., Srinivasan, S., Th., J., McDonald, I., Meixner, M., Zaritsky, D., Gordon, K. D., Kemper, F., Babler, B., Block, M., Bracker, S., Engelbracht, C. W., Hora, J., Indebetouw, R., Meade, M., Misselt, K., Robitaille, T., Sewiło, M., Shiao, B., & Whitney, B. (2012). Erratum: Surveying the agents of galaxy evolution in the tidally stripped, low-metallicity small magellanic cloud (SAGE-SMC). II. Cool evolved stars (The Astronomical Journal (2011) 142 (103)). Astronomical Journal, 143(5).
• Bradac, M., Vanzella, E., Hall, N., Treu, T., Fontana, A., Gonzalez, A. H., Clowe, D., Zaritsky, D., Stiavelli, M., & Clement, B. (2012). SPECTROSCOPIC CONFIRMATION OF A z=6.740 GALAXY BEHIND THE BULLET CLUSTER. ASTROPHYSICAL JOURNAL LETTERS, 755(1).
• Bradač, M., Vanzella, E., Hall, N., Treu, T., Fontana, A., Gonzalez, A. H., Clowe, D., Zaritsky, D., Stiavelli, M., & Clément, B. (2012). Spectroscopic confirmation of a z = 6.740 galaxy behind the bullet cluster. Astrophysical Journal Letters, 755(1).
  More info

  Abstract: We present the first results of our spectroscopic follow-up of 6.5 < z < 10 candidate galaxies behind clusters of galaxies.We report the spectroscopic confirmation of an intrinsically faint Lyman break galaxy (LBG) identified as a z850LP-band dropout behind the Bullet Cluster.We detect an emission line at λ = 9412 Å at>5σ significance using a 16 hr long exposure with FORS2 VLT. Based on the absence of flux in bluer broadband filters, the blue color of the source, and the absence of additional lines, we identify the line as Lyα at z = 6.740±0.003. The integrated line flux is f = (0.7±0.1±0.3)×10 -17 erg-1 s-1 cm-2 (the uncertainties are due to random and flux calibration errors, respectively) making it the faintest Lya flux detected at these redshifts. Given the magnification of μ = 3.0 ± 0.2 the intrinsic (corrected for lensing) flux is fint = (0.23 ± 0.03 ± 0.10 ± 0.02) × 10-17 erg-1 s-1 cm-2 (additional uncertainty due to magnification), which is ∼2-3 times fainter than other such measurements in z ∼ 7 galaxies. The intrinsic H 160W-band magnitude of the object is mint H160W = 27.57 ± 0.17, corresponding to 0.5L* for LBGs at these redshifts. The galaxy is one of the two sub-L* LBG galaxies spectroscopically confirmed at these high redshifts (the other is also a lensed z = 7.045 galaxy), making it a valuable probe for the neutral hydrogen fraction in the early universe. © 2012. The American Astronomical Society. All rights reserved.
• Clowe, D., Markevitch, M., Bradac, M., Gonzalez, A. H., Chung, S. M., Massey, R., & Zaritsky, D. (2012). ON DARK PEAKS AND MISSING MASS: A WEAK-LENSING MASS RECONSTRUCTION OF THE MERGING CLUSTER SYSTEM A520. ASTROPHYSICAL JOURNAL, 758(2).
• Clowe, D., Markevitch, M., Bradač, M., Gonzalez, A. H., Chung, S. M., Massey, R., & Zaritsky, D. (2012). On dark peaks and missing mass: A weak-lensing mass reconstruction of the merging cluster system A520. Astrophysical Journal, 758(2).
  More info

  Abstract: Merging clusters of galaxies are unique in their power to directly probe and place limits on the self-interaction cross-section of dark matter. Detailed observations of several merging clusters have shown the intracluster gas to be displaced from the centroids of dark matter and galaxy density by ram pressure, while the latter components are spatially coincident, consistent with collisionless dark matter. This has been used to place upper limits on the dark matter particle self-interaction cross-section of order 1cm 2 g -1. The cluster A520 has been seen as a possible exception. We revisit A520 presenting new Hubble Space Telescope Advanced Camera for Surveys mosaic images and a Magellan image set. We perform a detailed weak-lensing analysis and show that the weak-lensing mass measurements and morphologies of the core galaxy-filled structures are mostly in good agreement with previous works. There is, however, one significant difference: We do not detect the previously claimed "dark core" that contains excess mass with no significant galaxy overdensity at the location of the X-ray plasma. This peak has been suggested to be indicative of a large self-interaction cross-section for dark matter (at least 5σ larger than the upper limit of 0.7 cm 2 g -1 determined by observations of the Bullet Cluster). We find no such indication and instead find that the mass distribution of A520, after subtraction of the X-ray plasma mass, is in good agreement with the luminosity distribution of the cluster galaxies. We conclude that A520 shows no evidence to contradict the collisionless dark matter scenario. © 2012. The American Astronomical Society. All rights reserved.
• Eskew, M., Zaritsky, D., & Meidt, S. (2012). CONVERTING FROM 3.6 AND 4.5 mu m FLUXES TO STELLAR MASS. ASTRONOMICAL JOURNAL, 143(6).
• Eskew, M., Zaritsky, D., & Meidt, S. (2012). Converting from 3.6 and 4.5μm fluxes to stellar mass. Astronomical Journal, 143(6).
  More info

  Abstract: We use high spatial resolution maps of stellar mass and infrared flux of the Large Magellanic Cloud (LMC) to calibrate a conversion between 3.6 and 4.5μm fluxes and stellar mass, M * = 10 5.65 F 2.853.6 F -1.854.5(D/0.05) 2 M , where fluxes are in Jy and D is the luminosity distance to the source in Mpc, and to provide an approximate empirical estimate of the fractional internal uncertainty in M * of , where N is the number of stars in the region. We find evidence that young stars and hot dust contaminate the measurements, but attempts to remove this contamination using data that are far superior to what are generally available for unresolved galaxies resulted in marginal gains in accuracy. The scatter among mass estimates for regions in the LMC is comparable to that found by previous investigators when modeling composite populations, and so we conclude that our simple conversion is as precise as possible for the data and models currently available. Our results allow for a reasonably bottom-heavy initial mass function, such as Salpeter or heavier, and moderately disfavor lighter versions such as a diet-Salpeter or Chabrier initial mass function. © 2012 The American Astronomical Society. All rights reserved.
• Gonzalez, A. H., Zaritsky, D., & Zabludoff, A. I. (2012). A census of baryons in galaxy clusters and groups. ASTROPHYSICAL JOURNAL, 666(1), 147-155.
• Graham, M. L., Sand, D. J., Bildfell, C. J., Pritchet, C. J., Zaritsky, D., Hoekstra, H., Just, D. W., Herbert-Fort, S., Sivanandam, S., & Foley, R. J. (2012). The type II supernova rate in z ∼ 0.1 galaxy clusters from the multi-EPOCH nearby cluster survey. Astrophysical Journal, 753(1).
  More info

  Abstract: We present seven spectroscopically confirmed Type II cluster supernovae (SNeII) discovered in the Multi-Epoch Nearby Cluster Survey, a supernova survey targeting 57 low-redshift 0.05 < z < 0.15 galaxy clusters with the Canada-France-Hawaii Telescope. We find the rate of Type II supernovae within R 200 of z 0.1 galaxy clusters to be 0.026 +0.085- 0.018(stat) +0.003- 0.001(sys) SNuM. Surprisingly, one SNII is in a red-sequence host galaxy that shows no clear evidence of recent star formation (SF). This is unambiguous evidence in support of ongoing, low-level SF in at least some cluster elliptical galaxies, and illustrates that galaxies that appear to be quiescent cannot be assumed to host only Type Ia SNe. Based on this single SNII we make the first measurement of the SNII rate in red-sequence galaxies, and find it to be 0.007 +0.014- 0.007(stat) +0.009- 0.001(sys) SNuM. We also make the first derivation of cluster specific star formation rates (sSFR) from cluster SNII rates. We find that for all galaxy types the sSFR is 5.1 +15.8- 3.1(stat) ± 0.9(sys) M o yr -1 (10 12 M o) -1, and for red-sequence galaxies only it is 2.0 +4.2- 0.9(stat) ± 0.4(sys) M o yr -1 (10 12 M o) -1. These values agree with SFRs measured from infrared and ultraviolet photometry, and Hα emission from optical spectroscopy. Additionally, we use the SFR derived from our SNII rate to show that although a small fraction of cluster Type Ia SNe may originate in the young stellar population and experience a short delay time, these results do not preclude the use of cluster SNIa rates to derive the late-time delay time distribution for SNeIa. © © 2012. The American Astronomical Society. All rights reserved.
• Guennou, L., Adami, C., Rocha, C. D., Durret, F., Ulmer, M. P., Allam, S., Basa, S., Benoist, C., Biviano, A., Clowe, D., Gavazzi, R., Halliday, C., Ilbert, O., Johnston, D., Just, D., Kron, R., Kubo, J. M., Brun, V. L., Marshall, P., , Mazure, A., et al. (2012). Intracluster light in clusters of galaxies at redshifts 0.4 < z < 0.8. Astronomy and Astrophysics, 537.
  More info

  Abstract: Context. The study of intracluster light (ICL) can help us to understand the mechanisms taking place in galaxy clusters, and to place constraints on the cluster formation history and physical properties. However, owing to the intrinsic faintness of ICL emission, most searches and detailed studies of ICL have been limited to redshifts z < 0.4. Aims. To help us extend our knowledge of ICL properties to higher redshifts and study the evolution of ICL with redshift, we search for ICL in a subsample of ten clusters detected by the ESO Distant Cluster Survey (EDisCS), at redshifts 0.4 < z < 0.8, that are also part of our DAFT/FADA Survey. Methods. We analyze the ICL by applying the OV WAV package, a wavelet-based technique, to deep HST ACS images in the F814W filter and to V-band VLT/FORS2 images of three clusters. Detection levels are assessed as a function of the diffuse light source surface brightness using simulations. Results. In the F814W filter images, we detect diffuse light sources in all the clusters, with typical sizes of a few tens of kpc (assuming that they are at the cluster redshifts). The ICL detected by stacking the ten F814W images shows an 8σ detection in the source center extending over a ∼50 × 50 kpc 2 area, with a total absolute magnitude of-21.6 in the F814W filter, equivalent to about two L * galaxies per cluster. We find a weak correlation between the total F814W absolute magnitude of the ICL and the cluster velocity dispersion and mass. There is no apparent correlation between the cluster mass-to-light ratio (M/L) and the amount of ICL, and no evidence of any preferential orientation in the ICL source distribution. We find no strong variation in the amount of ICL between z = 0 and z = 0.8. In addition, we find wavelet-detected compact objects (WDCOs) in the three clusters for which data in two bands are available; these objects are probably very faint compact galaxies that in some cases are members of the respective clusters and comparable to the faint dwarf galaxies of the Local Group. Conclusions. We show that the ICL is prevalent in clusters at least up to redshift z = 0.8. In the future, we propose to detect the ICL at even higher redshifts, to determine wether there is a particular stage of cluster evolution where it was stripped from galaxies and spread into the intracluster medium. © 2012 ESO.
• Hall, N., Bradac, M., Gonzalez, A. H., Treu, T., Clowe, D., Jones, C., Stiavelli, M., Zaritsky, D., Cuby, J., & Clement, B. (2012). USING THE BULLET CLUSTER AS A GRAVITATIONAL TELESCOPE TO STUDY z greater than or similar to 7 LYMAN BREAK GALAXIES. ASTROPHYSICAL JOURNAL, 745(2).
• Hall, N., Bradač, M., Gonzalez, A. H., Treu, T., Clowe, D., Jones, C., Stiavelli, M., Zaritsky, D., Cuby, J., & Clément, B. (2012). Using the bullet cluster as a gravitational telescope to study z ≳ 7 Lyman break galaxies. Astrophysical Journal, 745(2).
  More info

  Abstract: We use imaging obtained with the Hubble Space Telescope Wide Field Camera 3 to search for z 850 dropouts at z ∼ 7 and J 110 dropouts at z ∼ 9 lensed by the Bullet Cluster. In total we find 10 z 850 dropouts in our 8.27 arcmin 2 field. Using magnification maps from a combined weak- and strong-lensing mass reconstruction of the Bullet Cluster and correcting for estimated completeness levels, we calculate the surface density and luminosity function of our z 850 dropouts as a function of intrinsic (accounting for magnification) magnitude. We find results consistent with published blank field surveys, despite using much shallower data, and demonstrate the effectiveness of cluster surveys in the search for z ∼ 7 galaxies. © 2012. The American Astronomical Society. All rights reserved.
• Herbert-Fort, S., Zaritsky, D., Moustakas, J., Di, P. A., Pogge, R. W., & Ragazzoni, R. (2012). STAR CLUSTER POPULATIONS IN THE OUTER DISKS OF NEARBY GALAXIES. ASTROPHYSICAL JOURNAL, 754(2).
• Herbert-Fort, S., Zaritsky, D., Moustakas, J., Paola, A. D., Pogge, R. W., & Ragazzoni, R. (2012). Star cluster populations in the outer disks of nearby galaxies. Astrophysical Journal, 754(2).
  More info

  Abstract: We present a Large Binocular Telescope imaging study that characterizes the star cluster component of nearby galaxy outer disks (beyond the optical radius R 25). Expanding on the pilot project of Herbert-Fort et al., we present deep (27.5 mag V-band point-source limiting magnitude) U- and V-band imaging of six galaxies: IC 4182, NGC3351, NGC4736, NGC4826, NGC5474, and NGC6503. We find that the outer disk of each galaxy is populated with marginally resolved star clusters with masses 10 3 M and ages up to 1Gyr (masses and ages are limited by the depth of our imaging and uncertainties are large given how photometry can be strongly affected by the presence or absence of a few stars in such low-mass systems), and that they are typically found out to at least 2 R 25 but sometimes as far as 3-4 R 25 - even beyond the apparent H I disk. The mean rate of cluster formation for 1 R 25 ≤ R ≤ 1.5 R 25 is at least one every 2.5Myr and the clusters are spatially correlated with the H I, most strongly with higher density gas near the periphery of the optical disk and with lower density neutral gas at the H I disk periphery. We hypothesize that the clusters near the edge of the optical disk are formed in the extension of spiral structure from the inner disk and are a fairly consistent phenomenon and that the clusters formed at the periphery of the H I disk are the result of accretion episodes. © 2012. The American Astronomical Society. All rights reserved..
• Kim, T., Sheth, K., Hinz, J. L., Lee, M. G., Zaritsky, D., Gadotti, D. A., Knapen, J. H., Schinnerer, E., Ho, L. C., Laurikainen, E., Salo, H., Athanassoula, E., Bosma, A., Swardt, B. D., Muñoz-Mateos, J., Madore, B. F., Comerón, S., Regan, M. W., Menéndez-Delmestre, K., , Gil, A., et al. (2012). Early-type galaxies with tidal debris and their scaling relations in the Spitzer Survey of Stellar Structure in Galaxies (S ⁴G). Astrophysical Journal, 753(1).
  More info

  Abstract: Tidal debris around galaxies can yield important clues on their evolution. We have identified tidal debris in 11 early-type galaxies (T ≤ 0) from a sample of 65 early types drawn from the Spitzer Survey of Stellar Structure in Galaxies (S 4G). The tidal debris includes features such as shells, ripples, and tidal tails. A variety of techniques, including two-dimensional decomposition of galactic structures, were used to quantify the residual tidal features. The tidal debris contributes ∼ 3%-10% to the total 3.6 μm luminosity of the host galaxy. Structural parameters of the galaxies were estimated using two-dimensional profile fitting. We investigate the locations of galaxies with tidal debris in the fundamental plane and Kormendy relation. We find that galaxies with tidal debris lie within the scatter of early-type galaxies without tidal features. Assuming that the tidal debris is indicative of recent gravitational interaction or merger, this suggests that these galaxies have either undergone minor merging events so that the overall structural properties of the galaxies are not significantly altered, or they have undergone a major merging events but already have experienced sufficient relaxation and phase mixing so that their structural properties become similar to those of the non-interacting early-type galaxies. © 2012. The American Astronomical Society. All rights reserved.
• Kim, T., Sheth, K., Hinz, J. L., Lee, M. G., Zaritsky, D., Gadotti, D. A., Knapen, J. H., Schinnerer, E., Ho, L. C., Laurikainen, E., Salo, H., Athanassoula, E., Bosma, A., de, S. B., Munoz-Mateos, J., Madore, B. F., Comeron, S., Regan, M. W., Menendez-Delmestre, K., , de, P., et al. (2012). EARLY-TYPE GALAXIES WITH TIDAL DEBRIS AND THEIR SCALING RELATIONS IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G). ASTROPHYSICAL JOURNAL, 753(1).
• Lucia, G. D., Weinmann, S., Poggianti, B. M., Aragón-Salamanca, A., & Zaritsky, D. (2012). The environmental history of group and cluster galaxies in a Λ cold dark matter universe. Monthly Notices of the Royal Astronomical Society, 423(2), 1277-1292.
  More info

  Abstract: We use publicly available galaxy merger trees, obtained applying semi-analytic techniques to a large high-resolution cosmological simulation, to study the environmental history of group and cluster galaxies. Our results highlight the existence of an intrinsic history bias which makes the nature versus nurture (as well as the mass versus environment) debate inherently ill posed. In particular, we show that (i) surviving massive satellites were accreted later than their less massive counterparts, from more massive haloes and (ii) the mixing of galaxy populations is incomplete during halo assembly, which creates a correlation between the time a galaxy becomes satellite and its present distance from the parent halo centre. The weakest trends are found for the most massive satellites, as a result of efficient dynamical friction and late formation times of massive haloes. A large fraction of the most massive group/cluster members are accreted on to the main progenitor of the final halo as central galaxies, while about half of the galaxies with low and intermediate stellar masses are accreted as satellites. Large fractions of group and cluster galaxies (in particular those of low stellar mass) have therefore been 'pre-processed' as satellites of groups with mass ∼10 13M ⊙. To quantify the relevance of hierarchical structure growth on the observed environmental trends, we have considered observational estimates of the passive galaxy fractions and their variation as a function of halo mass and clustercentric distance. Comparisons with our theoretical predictions require relatively long times (∼5-7 Gyr) for the suppression of star formation in group and cluster satellites. It is unclear how such a gentle mode of strangulation can be achieved by simply relaxing the assumption of instantaneous stripping of the hot gas reservoir associated with accreting galaxies, or if the difficulties encountered by recent galaxy formation models in reproducing the observed trends signal a more fundamental problem with the treatment of star formation and feedback in these galaxies. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.
• Meidt, S. E., Schinnerer, E., Knapen, J. H., Bosma, A., Athanassoula, E., Sheth, K., Buta, R. J., Zaritsky, D., Laurikainen, E., Elmegreen, D., Elmegreen, B. G., Gadotti, D. A., Salo, H., Regan, M., Ho, L. C., Madore, B. F., Hinz, J. L., Skibba, R. A., Gil, A., , Mũoz-Mateos, J., et al. (2012). Reconstructing the stellar mass distributions of galaxies using S ⁴G IRAC 3.6 and 4.5 μm images. I. Correcting for contamination by polycyclic aromatic hydrocarbons, hot dust, and intermediate-age stars. Astrophysical Journal, 744(1).
  More info

  Abstract: With the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 μm images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 μm bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 μm, which is dominated by the broad PAH feature. Using the measured 3.6 μm/8 μm ratio to select individual contaminants, we find that hot dust and PAHs together contribute between ∼5% and 15% to the integrated light at 3.6 μm, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information and are ideally suited for tracing stellar mass, as will be the focus in a companion paper.
• Sand, D. J., Graham, M. L., Bildfell, C., Zaritsky, D., Pritchet, C., Hoekstra, H., Just, D. W., Herbert-Fort, S., Sivanandam, S., Foley, R. J., & Mahdavi, A. (2012). THE MULTI-EPOCH NEARBY CLUSTER SURVEY: TYPE Ia SUPERNOVA RATE MEASUREMENT IN z similar to 0.1 CLUSTERS AND THE LATE-TIME DELAY TIME DISTRIBUTION. ASTROPHYSICAL JOURNAL, 746(2).
• Sand, D. J., Graham, M. L., Bildfell, C., Zaritsky, D., Pritchet, C., Hoekstra, H., Just, D. W., Herbert-Fort, S., Sivanandam, S., Foley, R. J., & Mahdavi, A. (2012). The Multi-Epoch Nearby Cluster Survey: Type Ia supernova rate measurement in z 0.1 clusters and the late-time delay time distribution. Astrophysical Journal, 746(2).
  More info

  Abstract: We describe the Multi-Epoch Nearby Cluster Survey, designed to measure the cluster Type Ia supernova (SN Ia) rate in a sample of 57 X-ray selected galaxy clusters, with redshifts of 0.05 < z < 0.15. Utilizing our real-time analysis pipeline, we spectroscopically confirmed twenty-three cluster SNe Ia, four of which were intracluster events. Using our deep Canada-France-Hawaii Telescope/MegaCam imaging, we measured total stellar luminosities in each of our galaxy clusters, and we performed detailed supernova (SN) detection efficiency simulations. Bringing these ingredients together, we measure an overall cluster SN Ia rate within R 200 (1Mpc) of 0.042 +0.012-0.010+0.010-0.008 SNuM (0.049 +0.016-0.014+0.005-0.004 SNuM) and an SN Ia rate within red-sequence galaxies of 0.041 +0.015-0.015+0.005-0.010 SNuM (0.041 +0.019-0.015+0.005-0.004 SNuM). The red-sequence SN Ia rate is consistent with published rates in early-type/elliptical galaxies in the "field." Using our red-sequence SN Ia rate, and other cluster SN measurements in early-type galaxies up to z 1, we derive the late-time (>2Gyr) delay time distribution (DTD) of SN Ia assuming a cluster early-type galaxy star formation epoch of z f = 3. Assuming a power-law form for the DTD, Ψ(t)t s , we find s = -1.62 0.54. This result is consistent with predictions for the double degenerate SN Ia progenitor scenario (s ∼ -1) and is also in line with recent calculations for the double detonation explosion mechanism (s ∼ -2). The most recent calculations of the single degenerate scenario DTD predicts an order-of-magnitude drop-off in SN Ia rate ∼6-7Gyr after stellar formation, and the observed cluster rates cannot rule this out. © 2012 The American Astronomical Society. All rights reserved.
• Sand, D. J., Strader, J., Willman, B., Zaritsky, D., McLeod, B., Caldwell, N., Seth, A., & Olszewski, E. (2012). TIDAL SIGNATURES IN THE FAINTEST MILKY WAY SATELLITES: THE DETAILED PROPERTIES OF LEO V, PISCES II, AND CANES VENATICI II. ASTROPHYSICAL JOURNAL, 756(1).
• Sand, D. J., Zaritsky, D., Olszewski, E. W., Zaritsky, D., Willman, B., Strader, J., Seth, A. C., Sand, D. J., Olszewski, E. W., Mcleod, B., & Caldwell, N. (2012). Tidal signatures in the faintest milky way satellites: The detailed properties of Leo V, Pisces II, and Canes Venatici II. The Astrophysical Journal, 756(1), 79. doi:10.1088/0004-637x/756/1/79
  More info

  We present deep wide-field photometry of three recently discovered faint Milky Way (MW) satellites: Leo V, Pisces II, and Canes Venatici II. Our main goals are to study the structure and star formation history of these dwarfs; we also search for signs of tidal disturbance. The three satellites have similar half-light radii ({approx}60-90 pc) but a wide range of ellipticities. Both Leo V and CVn II show hints of stream-like overdensities at large radii. An analysis of the satellite color-magnitude diagrams shows that all three objects are old (>10 Gyr) and metal-poor ([Fe/H] {approx} -2), though neither the models nor the data have sufficient precision to assess when the satellites formed with respect to cosmic reionization. The lack of an observed younger stellar population ({approx} 150 kpc. We present a new compilation of structural data for all MW satellite galaxies and use it to compare the properties of classical dwarfs to the ultra-faints. The ellipticity distribution of the two groups is consistent at the {approx}2{sigma} level. However, the faintest satellites tend to be more aligned toward the Galactic Center, and those satellites with the highest ellipticitymore » ({approx}> 0.4) have orientations ({Delta}{theta}{sub GC}) in the range 20 Degree-Sign {approx}< {Delta}{theta}{sub GC} {approx}< 40 Degree-Sign . This latter observation is in rough agreement with predictions from simulations of dwarf galaxies that have lost a significant fraction of their dark matter halos and are being tidally stripped.« less
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2012). Testing Distance Estimators with the Fundamental Manifold. The Astrophysical Journal, 748(1), 15. doi:10.1088/0004-637x/748/1/15
  More info

  We demonstrate how the Fundamental Manifold (FM) can be used to cross-calibrate distance estimators even when those standard candles are not found in the same galaxy. Such an approach greatly increases the number of distance measurements that can be utilized to check for systematic distance errors and the types of estimators that can be compared. Here we compare distances obtained using Type Ia supernova (SN Ia), Cepheids, surface brightness fluctuations, the luminosity of the tip of the red giant branch, circumnuclear masers, eclipsing binaries, RR Lyrae stars, and the planetary nebulae luminosity functions. We find no significant discrepancies (differences are
• Zaritsky, D. (2012). Implications and Applications of Kinematic Galaxy Scaling Relations. International Scholarly Research Notices, 2012, 1-15. doi:10.5402/2012/189625
  More info

  Galaxy scaling relations, which describe a connection between ostensibly unrelated physical characteristics, testify to an underlying order in galaxy formation that requires understanding. I review the development of a scaling relation that (1) unites the well-known fundamental plane (FP) relation of giant elliptical galaxies and Tully-Fisher (TF) relation of disk galaxies, (2) fits low mass spheroidal galaxies, including the ultrafaint satellites of our galaxy, (3) explains the apparent shift of lenticular galaxies relative to both FP or TF, (4) describes all stellar dynamical systems, including systems with no dark matter (stellar clusters), (5) associates explicitly the numerical coefficients that account for the apparent tilt of the FP away from the expectation drawn from the virial theorem with variations in the total mass-to-light ratio of galaxies within the half-light radius, (6) connects with results that demonstrate the robustness of mass estimators when applied at the half-light radius, and (7) results in smaller scatter for disk galaxies than the TF relation. I review two applications: (1) the cross-calibration of distance measurement methods and (2) the determination of mass-to-light ratios of simple stellar populations and implications for the stellar initial mass function.
• Zaritsky, D., & Gonzalez, A. (2012). On the incidence of strong gravitational lensing by clusters in the Las Campanas Distant Cluster Survey. ASTROPHYSICAL JOURNAL, 584(2), 691-701.
• Zaritsky, D., Colucci, J. E., Pessev, P. M., Bernstein, R. A., & Chandar, R. (2012). EVIDENCE FOR TWO DISTINCT STELLAR INITIAL MASS FUNCTIONS. ASTROPHYSICAL JOURNAL, 761(2).
• Zaritsky, D., Colucci, J. E., Pessev, P. M., Bernstein, R. A., & Chandar, R. (2012). Evidence for two distinct stellar initial mass functions. Astrophysical Journal, 761(2).
  More info

  Abstract: We present velocity dispersion measurements of 20 Local Group stellar clusters (7 < log(age [yr])
• Zaritsky, D., Skibba, R. A., Sheth, K., Seibert, M., Schinnerer, E., Salo, H., Regan, M. W., Paz, A. G., Munoz-mateos, J. C., Mizusawa, T., Menendez-delmestre, K., Meidt, S. E., Madore, B. F., Laurikainen, E., Laine, J., Knapen, J. H., Kim, T., Ho, L. C., Hinz, J. L., , Gadotti, D. A., et al. (2012). RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S4G IRAC 3.6 AND 4.5 μm IMAGES. I. CORRECTING FOR CONTAMINATION BY POLYCYCLIC AROMATIC HYDROCARBONS, HOT DUST, AND INTERMEDIATE-AGE STARS. The Astrophysical Journal, 744(1), 17. doi:10.1088/0004-637x/744/1/17
  More info

  With the aim of constructing accurate two-dimensional maps of the stellar mass distribution in nearby galaxies from Spitzer Survey of Stellar Structure in Galaxies 3.6 and 4.5 μm images, we report on the separation of the light from old stars from the emission contributed by contaminants. Results for a small sample of six disk galaxies (NGC 1566, NGC 2976, NGC 3031, NGC 3184, NGC 4321, and NGC 5194) with a range of morphological properties, dust content, and star formation histories are presented to demonstrate our approach. To isolate the old stellar light from contaminant emission (e.g., hot dust and the 3.3 μm polycyclic aromatic hydrocarbon (PAH) feature) in the IRAC 3.6 and 4.5 μm bands we use an independent component analysis (ICA) technique designed to separate statistically independent source distributions, maximizing the distinction in the [3.6]-[4.5] colors of the sources. The technique also removes emission from evolved red objects with a low mass-to-light ratio, such as asymptotic giant branch (AGB) and red supergiant (RSG) stars, revealing maps of the underlying old distribution of light with [3.6]-[4.5] colors consistent with the colors of K and M giants. The contaminants are studied by comparison with the non-stellar emission imaged at 8 μm, which is dominated by the broad PAH feature. Using the measured 3.6 μm/8 μm ratio to select individual contaminants, we find that hot dust and PAHs together contribute between ~5% and 15% to the integrated light at 3.6 μm, while light from regions dominated by intermediate-age (AGB and RSG) stars accounts for only 1%-5%. Locally, however, the contribution from either contaminant can reach much higher levels; dust contributes on average 22% to the emission in star-forming regions throughout the sample, while intermediate-age stars contribute upward of 50% in localized knots. The removal of these contaminants with ICA leaves maps of the old stellar disk that retain a high degree of structural information and are ideally suited for tracing stellar mass, as will be the focus in a companion paper.
• Zaritsky, D., Vulcani, B., Poggianti, B. M., Milvang-jensen, B., Linden, A. V., Johnson, O., Jablonka, P., Fritz, J., & Aragon-salamanca, A. (2012). Cl 1103.7–1245 at z = 0.96: the highest redshift galaxy cluster in the EDisCS survey. Astronomy and Astrophysics, 544, A104. doi:10.1051/0004-6361/201219397
  More info

  We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl 1103.7-1245 (z = 0.9580; sigma(clus) = 522 +/- 111 km s(-1)) we find a secondary structure at z = 0.9830, Cl 1103.7-1245c. We then characterize the galaxy properties in both systems, and find that they contain very different galaxy populations. The cluster Cl 1103.7-1245 hosts a mixture of passive elliptical galaxies and star-forming spirals and irregulars. In the secondary structure Cl 1103.7-1245c all galaxies are lower-mass star-forming irregulars and peculiars. In addition, we compare the galaxy populations in the Cl 1103.7-1245 z = 0.9580 cluster with those in lower redshift EDisCS clusters with similar velocity dispersions. We find that the properties of the galaxies in Cl 1103.7-1245 follow the evolutionary trends found at lower redshifts: the number of cluster members increases with time in line with the expected growth in cluster mass, and the fraction of passive early-type galaxies increases with time while star-forming late types become less dominant. Finally, we find that the mean stellar masses are similar in all clusters, suggesting that massive cluster galaxies were already present at z similar to 1.
• Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2012). TESTING DISTANCE ESTIMATORS WITH THE FUNDAMENTAL MANIFOLD. ASTROPHYSICAL JOURNAL, 748(1).
• c, M., Vanzella, E., Hall, N., Treu, T., Fontana, A., Gonzalez, A. H., Clowe, D., Zaritsky, D., Stiavelli, M., & Cl 'ement, B. (2012). Breaking Cosmic Dawn: The Faintest Galaxy Detected by the VLT. The Messenger, 150, 53-55.
• A., K., Zaritsky, D., Blum, R. D., Boyer, M. L., & Gordon, K. D. (2011). A population of accreted small magellanic cloud stars in the large magellanic cloud. Astrophysical Journal, 737(1).
  More info

  Abstract: We present an analysis of the stellar kinematics of the Large Magellanic Cloud (LMC) based on 5900 new and existing velocities of massive red supergiants, oxygen-rich and carbon-rich asymptotic giant branch (AGB) stars, and other giants. After correcting the line-of-sight velocities for theLMC's space motion and accounting for asymmetric drift in the AGB population, we derive a rotation curve that is consistent with all of the tracers used, as well as that of published H I data. The amplitude of the rotation curve is v 0 = 87 5km s-1 beyond a radius R 0 = 2.4 0.1kpc and has a position angle of the kinematic line of nodes of θ = 142°±5°. By examining the outliers from our fits, we identify a population of 376 stars, or ≳5% of our sample, that have line-of-sight velocities that apparently oppose the sense of rotation of theLMC disk. We find that these kinematically distinct stars are either counter-rotating in a plane closely aligned with theLMC disk, or rotating in the same sense as theLMC disk, but in a plane that is inclined by 54° ±2° to theLMC. Their kinematics clearly link them to two known H I arms, which have previously been interpreted as being pulled out from theLMC. We measure metallicities from the Ca triplet lines of 1000LMC field stars and 30 stars in the kinematically distinct population. For theLMC field, we find a median [Fe/H] = -0.56v0.02 with dispersion of 0.5 dex, while for the kinematically distinct stars the median [Fe/H] is -1.25 0.13 with a dispersion of 0.7 dex. The metallicity differences provide strong evidence that the kinematically distinct population originated in the Small Magellanic Cloud. This interpretation has the consequence that the H I arms kinematically associated with the stars are likely falling into theLMC, instead of being pulled out. © 2011. The American Astronomical Society. All rights reserved..
• Boyer, M. L., Srinivasan, S., Th., J., McDonald, I., Meixner, M., Zaritsky, D., Gordon, K. D., Kemper, F., Babler, B., Block, M., Bracker, S., Engelbracht, C. W., Hora, J., Indebetouw, R., Meade, M., Misselt, K., Robitaille, T., Sewiło, M., Shiao, B., & Whitney, B. (2011). Surveying the agents of galaxy evolution in the tidally stripped, low metallicity Small Magellanic Cloud (SAGE-SMC). II. Cool evolved stars. Astronomical Journal, 142(4).
  More info

  Abstract: We investigate the infrared (IR) properties of cool, evolved stars in the Small Magellanic Cloud (SMC), including the red giant branch (RGB) stars and the dust-producing red supergiant (RSG) and asymptotic giant branch (AGB) stars using observations from the Spitzer Space Telescope Legacy program entitled "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity SMC," or SAGE-SMC. The survey includes, for the first time, full spatial coverage of the SMC bar, wing, and tail regions at IR wavelengths (3.6-160 μm). We identify evolved stars using a combination of near-IR and mid-IR photometry and point out a new feature in the mid-IR color-magnitude diagram that may be due to particularly dusty O-rich AGB stars. We find that the RSG and AGB stars each contribute ≈ 20% of the global SMC flux (extended + point-source) at 3.6 μm, which emphasizes the importance of both stellar types to the integrated flux of distant metal-poor galaxies. The equivalent SAGE survey of the higher-metallicity Large Magellanic Cloud (SAGE-LMC) allows us to explore the influence of metallicity on dust production. We find that the SMC RSG stars are less likely to produce a large amount of dust (as indicated by the [3.6] - [8] color). There is a higher fraction of carbon-rich stars in the SMC, and these stars appear to reach colors as red as their LMC counterparts, indicating that C-rich dust forms efficiently in both galaxies. A preliminary estimate of the dust production in AGB and RSG stars reveals that the extreme C-rich AGB stars dominate the dust input in both galaxies, and that the O-rich stars may play a larger role in the LMC than in the SMC. © 2011. The American Astronomical Society. All rights reserved.
• Boyer, M. L., Srinivasan, S., van, L., McDonald, I., Meixner, M., Zaritsky, D., Gordon, K. D., Kemper, F., Babler, B., Block, M., Bracker, S., Engelbracht, C. W., Hora, J., Indebetouw, R., Meade, M., Misselt, K., Robitaille, T., Sewillo, M., Shiao, B., & Whitney, B. (2011). SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). II. COOL EVOLVED STARS. ASTRONOMICAL JOURNAL, 142(4).
• Comeron, S., Elmegreen, B. G., Knapen, J. H., Sheth, K., Hinz, J. L., Regan, M. W., Gil, d., Munoz-Mateos, J., Menendez-Delmestre, K., Seibert, M., Kim, T., Mizusawa, T., Laurikainen, E., Salo, H., Laine, J., Athanassoula, E., Bosma, A., Buta, R. J., Gadotti, D. A., , Ho, L. C., et al. (2011). THE UNUSUAL VERTICAL MASS DISTRIBUTION OF NGC 4013 SEEN THROUGH THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G). ASTROPHYSICAL JOURNAL LETTERS, 738(2).
• Comerón, S., Elmegreen, B. G., Knapen, J. H., Sheth, K., Hinz, J. L., Regan, M. W., Gil, A., Mũoz-Mateos, J., Menéndez-Delmestre, K., Seibert, M., Kim, T., Mizusawa, T., Laurikainen, E., Salo, H., Laine, J., Athanassoula, E., Bosma, A., Buta, R. J., Gadotti, D. A., , Ho, L. C., et al. (2011). The unusual vertical mass distribution of NGC 4013 seen through the spitzer survey of stellar structure in galaxies (S⁴G). Astrophysical Journal Letters, 738(2).
  More info

  Abstract: NGC 4013 is a nearby Sb edge-on galaxy known for its "prodigious" H I warp and its "giant" tidal stream. Previous work on this unusual object shows that it cannot be fitted satisfactorily by a canonical thin+thick disk structure. We have produced a new decomposition of NGC 4013, considering three stellar flattened components (thin+thick disk plus an extra and more extended component) and one gaseous disk. All four components are considered to be gravitationally coupled and isothermal. To do so, we have used the 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. We find evidence for NGC 4013 indeed having a thin and a thick disk and an extra flattened component. This smooth and extended component (scale height z EC 3kpc) could be interpreted as a thick disk or as a squashed ellipsoidal halo and contains 20% of the total mass of all three stellar components. We argue it is unlikely to be related to the ongoing merger or due to the off-plane stars from a warp in the other two disk components. Instead, we favor a scenario in which the thick disk and the extended component were formed in a two-stage process, in which an initially thick disk has been dynamically heated by a merger soon enough in the galaxy history to have a new thick disk formed within it. © 2011. The American Astronomical Society. All rights reserved..
• Elmegreen, D. M., Elmegreen, B. G., Yau, A., Athanassoula, E., Bosma, A., Buta, R. J., Helou, G., Ho, L. C., Gadotti, D. A., Knapen, J. H., Laurikainen, E., Madore, B. F., Masters, K. L., Meidt, S. E., Menendez-Delmestre, K., Regan, M. W., Salo, H., Sheth, K., Zaritsky, D., , Aravena, M., et al. (2011). GRAND DESIGN AND FLOCCULENT SPIRALS IN THE SPITZER SURVEY OF STELLAR STRUCTURE IN GALAXIES (S(4)G). ASTROPHYSICAL JOURNAL, 737(1).
• Elmegreen, D. M., Elmegreen, B. G., Yau, A., Athanassoula, E., Bosma, A., Buta, R. J., Helou, G., Ho, L. C., Gadotti, D. A., Knapen, J. H., Laurikainen, E., Madore, B. F., Masters, K. L., Meidt, S. E., Menéndez-Delmestre, K., Regan, M. W., Salo, H., Sheth, K., Zaritsky, D., , Aravena, M., et al. (2011). Grand design and flocculent spirals in the spitzer survey of stellar structure in galaxies (S⁴G). Astrophysical Journal, 737(1).
  More info

  Abstract: Spiral arm properties of 46 galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G) were measured at 3.6 μm, where extinction is small and the old stars dominate. The sample includes flocculent, multiple arm, and grand design types with a wide range of Hubble and bar types. We find that most optically flocculent galaxies are also flocculent in the mid-IR because of star formation uncorrelated with stellar density waves, whereas multiple arm and grand design galaxies have underlying stellar waves. Arm-interarm contrasts increase from flocculent to multiple arm to grand design galaxies and with later Hubble types. Structure can be traced further out in the disk than in previous surveys. Some spirals peak at mid-radius while others continuously rise or fall, depending on Hubble and bar type. We find evidence for regular and symmetric modulations of the arm strength in NGC4321. Bars tend to be long, high amplitude, and flat-profiled in early-type spirals, with arm contrasts that decrease with radius beyond the end of the bar, and they tend to be short, low amplitude, and exponential-profiled in late Hubble types, with arm contrasts that are constant or increase with radius. Longer bars tend to have larger amplitudes and stronger arms. © 2011. The American Astronomical Society. All rights reserved.
• Eskew, M., & Zaritsky, D. (2011). NEARBY GALAXIES IN MORE DISTANT CONTEXTS. ASTRONOMICAL JOURNAL, 141(2).
• Eskew, M., & Zaritsky, D. (2011). Nearby galaxies in more distant contexts. Astronomical Journal, 141(2).
  More info

  Abstract: We use published reconstructions of the star formation history (SFH) of the Large Magellanic Cloud (LMC), Small Magellanic Cloud, and NGC 300 from the analysis of resolved stellar populations to investigate where such galaxies might land on well-known extragalactic diagnostic plots over the galaxies' lifetime (assuming that nothing other than their stellar populations change). For example, we find that the evolution of these galaxies implies a complex evolution in the Tully-Fisher relation with look-back time and that the observed scatter is consistent with excursions these galaxies take as their stellar populations evolve. We find that the growth of stellar mass is weighted to early times, despite the strongly star-forming current nature of the three systems. Lastly, we find that these galaxies can take circuitous paths across the color-magnitude diagram. For example, it is possible, within the constraints provided by the current determination of its SFH, that the LMC reached the red sequence at intermediate age prior to ending back up on the blue cloud at the current time. Unfortunately, this behavior happens at sufficiently early times that our resolved SFH is crude and insufficiently constraining to convincingly demonstrate that this was the actual evolutionary path. The limited sample size precludes any general conclusions, but we present these as examples how we can bridge the study of resolved populations and the more distant universe. © 2011. The American Astronomical Society. All rights reserved.
• Freeland, E., Tran, K. H., Irwin, T., Giordano, L., Saintonge, A., Gonzalez, A. H., Zaritsky, D., & Just, D. (2011). DETECTION OF OUTFLOWING AND EXTRAPLANAR GAS IN DISKS IN AN ASSEMBLING GALAXY CLUSTER AT z=0.37. ASTROPHYSICAL JOURNAL LETTERS, 742(2).
• Freeland, E., Tran, K. H., Irwin, T., Giordano, L., Saintonge, A., Gonzalez, A. H., Zaritsky, D., & Just, D. (2011). Detection of outflowing and extraplanar gas in disks in an assembling galaxy cluster at z = 0.37. Astrophysical Journal Letters, 742(2).
  More info

  Abstract: We detect ionized gas characteristics indicative of winds in three disk-dominated galaxies that are members of a super-group at z = 0.37 that will merge to form a Coma-mass cluster. All three galaxies are IR luminous (L IR > 4 × 1010 L ⊙, SFR > 8 M ⊙ yr-1) and lie outside the X-ray cores of the galaxy groups. We find that the most IR-luminous galaxy has strong blueshifted and redshifted emission lines with velocities of ∼ ± 200 km s -1 and a third, blueshifted (900 km s-1) component. This galaxy's line widths (Hβ, [OIII]λ5007, [NII], Hα) correspond to velocities of 100-1000 km s-1. We detect extraplanar gas in two of the three galaxies with SFR >8 M ⊙ yr-1 whose orientations are approximately edge-on and which have integral field unit (IFU) spaxels off the stellar disk. IFU maps reveal that the extraplanar gas extends to rh ∼ 10kpc; [NII] and Hα line widths correspond to velocities of 200-400 km s-1 in the disk and decrease to ∼ 50-150 km s-1 above the disk. Multi-wavelength observations indicate that the emission is dominated by star formation. Including the most IR-luminous galaxy we find that 18% of supergroup members with SFR >8 M ⊙ yr-1 show ionized gas characteristics indicative of outflows. This is a lower limit as showing that gas is outflowing in the remaining, moderately inclined, galaxies requires a non-trivial decoupling of contributions to the emission lines from rotational and turbulent motion. Ionized gas mass loss in these winds is ∼0.1 M ⊙ yr-1 for each galaxy, although the winds are likely to entrain significantly larger amounts of mass in neutral and molecular gases. © 2011. The American Astronomical Society. All rights reserved..
• Gonzalez, A., Zabludoff, A., & Zaritsky, D. (2011). Intracluster light in nearby galaxy clusters: Relationship to the halos of brightest cluster galaxies. ASTROPHYSICAL JOURNAL, 618(1), 195-213.
• Gordon, K. D., Meixner, M., Meade, M. R., Whitney, B., Engelbracht, C., Bot, C., Boyer, M. L., Lawton, B., Sewiło, M., Babler, B., Bernard, J. -., Bracker, S., Block, M., Blum, R., Bolatto, A., Bonanos, A., Harris, J., Hora, J. L., Indebetouw, R., , Misselt, K., et al. (2011). Surveying the agents of galaxy evolution in the tidally stripped, low metallicity Small Magellanic Cloud (SAGE-SMC). I. overview. Astronomical Journal, 142(4).
  More info

  Abstract: The Small Magellanic Cloud (SMC) provides a unique laboratory for the study of the lifecycle of dust given its low metallicity (1/5 solar) and relative proximity (∼60kpc). This motivated the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud) Spitzer Legacy program with the specific goals of studying the amount and type of dust in the present interstellar medium, the sources of dust in the winds of evolved stars, and how much dust is consumed in star formation. This program mapped the full SMC (30 deg2) including the body, wing, and tail in seven bands from 3.6 to 160 μm using IRAC and MIPS on the Spitzer Space Telescope. The data were reduced and mosaicked, and the point sources were measured using customized routines specific for large surveys. We have made the resulting mosaics and point-source catalogs available to the community. The infrared colors of the SMC are compared to those of other nearby galaxies and the 8 μm/24 μm ratio is somewhat lower than the average and the 70 μm/160 μm ratio is somewhat higher than the average. The global infrared spectral energy distribution (SED) shows that the SMC has approximately 1/3 the aromatic emission/polycyclic aromatic hydrocarbon abundance of most nearby galaxies. Infrared color-magnitude diagrams are given illustrating the distribution of different asymptotic giant branch stars and the locations of young stellar objects. Finally, the average SED of H II/star formation regions is compared to the equivalent Large Magellanic Cloud average H II/star formation region SED. These preliminary results will be expanded in detail in subsequent papers. © 2011. The American Astronomical Society. All rights reserved.
• Jaffe, Y. L., Aragon-Salamanca, A., De, L. G., Jablonka, P., Rudnick, G., Saglia, R., & Zaritsky, D. (2011). The colour-magnitude relation of elliptical and lenticular galaxies in the ESO Distant Cluster Survey. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 410(1), 280-292.
• Jaffe, Y. L., Aragon-Salamanca, A., Kuntschner, H., Bamford, S., Hoyos, C., De, L. G., Halliday, C., Milvang-Jensen, B., Poggianti, B., Rudnick, G., Saglia, R. P., Sanchez-Blazquez, P., & Zaritsky, D. (2011). The effect of the environment on the gas kinematics and the structure of distant galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 417(3), 1996-2019.
• Jaffé, Y. L., Aragón-Salamanca, A., Kuntschner, H., Bamford, S., Hoyos, C., Lucia, G. D., Halliday, C., Milvang-Jensen, B., Poggianti, B., Rudnick, G., Saglia, R. P., Sanchez-Blazquez, P., & Zaritsky, D. (2011). The effect of the environment on the gas kinematics and the structure of distant galaxies. Monthly Notices of the Royal Astronomical Society, 417(3), 1996-2019.
  More info

  Abstract: With the aim of distinguishing between possible physical mechanisms acting on galaxies when they fall into clusters, we study the properties of the gas and the stars in a sample of 422 emission-line galaxies from the European Southern Observatory Distant Cluster Survey in different environments up to z∼ 1. We identify galaxies with kinematical disturbances (from emission lines in their 2D spectra) and find that they are more frequent in clusters than in the field. The fraction of kinematically disturbed galaxies increases with cluster velocity dispersion and decreases with distance from the cluster centre, but remains constant with projected galaxy density. We also studied morphological disturbances in the stellar light from Hubble Space Telescope/F814W images, finding that the fraction of morphologically disturbed galaxies is similar in clusters, groups and the field. Moreover, there is little correlation between the presence of kinematically disturbed gas and morphological distortions. For the kinematically undisturbed galaxies, we find that the cluster and field Tully-Fisher relations are remarkably similar. In addition, we find that the kinematically disturbed galaxies show a suppressed specific star formation rate. There is also evidence indicating that the gas discs in cluster galaxies have been truncated, and therefore their star formation is more concentrated than in low-density environments. If spirals are the progenitors of cluster S0s, our findings imply that the physical mechanism transforming cluster galaxies efficiently disturbs the star-forming gas and reduces their specific star formation rate. Moreover, this star-forming gas is either removed more efficiently from the outskirts of the galaxies or is driven towards the centre (or both). In any case, this makes any remaining star formation more centrally concentrated, helping to build the bulges of S0s. These results, in addition to the finding that the transformation mechanism does not seem to induce strong morphological disturbances on the galaxies, suggest that the physical processes involved are related to the intracluster medium, with galaxy-galaxy interactions playing only a limited role in clusters. © 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS.
• Jaffé, Y. L., Aragón-Salamanca, A., Lucia, G. D., Jablonka, P., Rudnick, G., Saglia, R., & Zaritsky, D. (2011). The colour-magnitude relation of elliptical and lenticular galaxies in the ESO Distant Cluster Survey. Monthly Notices of the Royal Astronomical Society, 410(1), 280-292.
  More info

  Abstract: In this paper we study the colour-magnitude relation (CMR) for a sample of 172 morphologically classified elliptical and S0 cluster galaxies from the ESO Distant Cluster Survey (EDisCS) at 0.4 ≲z≲ 0.8. The intrinsic colour scatter about the CMR is very small (σint)= 0.076) in rest-frame U-V. However, there is a small minority of faint early-type galaxies (7 per cent) that are significantly bluer than the CMR. We observe no significant dependence of σint with redshift or cluster velocity dispersion. Because our sample is strictly morphologically selected, this implies that by the time cluster elliptical and S0 galaxies achieve their morphology, the vast majority have already joined the red sequence. The only exception seems to be the very small fraction of faint blue early types. Assuming that the intrinsic colour scatter is due to differences in stellar population ages, we estimate the galaxy formation redshift zF of each cluster and find that zF does not depend on the cluster velocity dispersion. However, zF increases weakly with cluster redshift within the EDisCS sample. This trend becomes very clear when higher redshift clusters from the literature are included. This suggests that, at any given redshift, in order to have a population of fully formed ellipticals and S0s they needed to have formed most of their stars {reversed tilde equals}2-4-Gyr prior to observation. That does not mean that all early-type galaxies in all clusters formed at these high redshifts. It means that the ones we see already having early-type morphologies also have reasonably old stellar populations. This is partly a manifestation of the 'progenitor bias', but also a consequence of the fact that the vast majority of the early-type galaxies in clusters (in particular the massive galaxies) were already red (i.e. already had old stellar populations) by the time they achieved their morphology. Elliptical and S0 galaxies exhibit very similar colour scatter, implying similar stellar population ages. The scarcity of blue S0s indicates that, if they are the descendants of spirals whose star formation has ceased, the parent galaxies were already red when they became S0s. This suggests the red spirals found preferentially in dense environments could be the progenitors of these S0s. We also find that fainter early-type galaxies finished forming their stars later (i.e. have smaller zF), consistent with the cluster red sequence being built over time and the brightest galaxies reaching the red sequence earlier than fainter ones. Combining the CMR scatter analysis with the observed evolution in the CMR zero-point we find that the early-type cluster galaxy population must have had their star formation truncated/stopped over an extended period δt≳ 1 Gyr. © 2010 The Authors. Journal compilation © 2010 RAS.
• Just, D. W., Zaritsky, D., Tran, K. H., Gonzalez, A. H., Kautsch, S. J., & Moustakas, J. (2011). A SEARCH FOR YOUNG STARS IN THE S0 GALAXIES OF A SUPER-GROUP AT z=0.37. ASTROPHYSICAL JOURNAL, 740(2).
• Just, D. W., Zaritsky, D., Tran, K. H., Gonzalez, A. H., Kautsch, S. J., & Moustakas, J. (2011). A search for young stars in the S0 galaxies of a super-group at z = 0.37. Astrophysical Journal, 740(2).
  More info

  Abstract: We analyze Galaxy Evolution Explorer UV data for a system of four gravitationally bound groups at z = 0.37, SG1120, which is destined to merge into a Coma-mass cluster by z = 0, to study how galaxy properties may change during cluster assembly. Of the 38 visually classified S0 galaxies, with masses ranging from log (M *)[M ⊙] 10-11, we detect only one in the near-UV (NUV) channel, a strongly star-forming S0 that is the brightest UV source with a measured redshift placing it in SG1120. Stacking the undetected S0 galaxies (which generally lie on or near the optical red sequence of SG1120) still results in no NUV/far-UV (FUV) detection (
• Olsen, K., Zaritsky, D., Blum, R. D., Boyer, M. L., & Gordon, K. D. (2011). A POPULATION OF ACCRETED SMALL MAGELLANIC CLOUD STARS IN THE LARGE MAGELLANIC CLOUD. ASTROPHYSICAL JOURNAL, 737(1).
• Sand, D. J., Graham, M. L., Bildfell, C., Foley, R. J., Pritchet, C., Zaritsky, D., Hoekstra, H., Just, D. W., Herbert-Fort, S., & Sivanandam, S. (2011). INTRACLUSTER SUPERNOVAE IN THE MULTI-EPOCH NEARBY CLUSTER SURVEY. ASTROPHYSICAL JOURNAL, 729(2).
• Sand, D. J., Graham, M. L., Bildfell, C., Foley, R. J., Pritchet, C., Zaritsky, D., Hoekstra, H., Just, D. W., Herbert-Fort, S., & Sivanandam, S. (2011). Intracluster supernovae in the multi-epoch nearby cluster survey. Astrophysical Journal, 729(2).
  More info

  Abstract: The Multi-Epoch Nearby Cluster Survey has discovered 23 cluster Type Ia supernovae (SNe Ia) in the 58 X-ray-selected galaxy clusters (0.05 ≲z≲ 0.15) surveyed. Four of our SN Ia events have no host galaxy on close inspection, and are likely intracluster SNe. Although one of the candidates, Abell399-3-14-0, appears to be associated in projection with the outskirts of a nearby red sequence galaxy, its velocity offset of 1000 km s-1 indicates that it is unbound and therefore an intracluster SN. Another of our candidates, Abell85-6-08-0, has a spectrum consistent with an SN1991bg-like object, suggesting that at least some portion of intracluster stars belong to an old stellar population. Deep image stacks at the location of the candidate intracluster SNe put upper limits on the luminosities of faint hosts, with Mr ≳ -13.0 mag and Mg ≳ -12.5 mag in all cases. For such limits, the fraction of the cluster luminosity in faint dwarfs below our detection limit is ≲0.1%, assuming a standard cluster luminosity function. All four events occurred within 600 kpc of the cluster center (projected), as defined by the position of the brightest cluster galaxy, and are more centrally concentrated than the cluster SN Ia population as a whole. After accounting for several observational biases that make intracluster SNe easier to discover and spectroscopically confirm, we calculate an intracluster stellar mass fraction of 0.16+0.13-0.09 (68% confidence limit) for all objects within R 200. If we assume that the intracluster stellar population is exclusively old, and the cluster galaxies themselves have a mix of stellar ages, we derive an upper limit on the intracluster stellar mass fraction of
• Velzen, S. V., Farrar, G. R., Gezari, S., Morrell, N., Zaritsky, D., Östman, L., Smith, M., Gelfand, J., & Drake, A. J. (2011). Optical Discovery of probable stellar tidal disruption flares. Astrophysical Journal, 741(2).
  More info

  Abstract: Using archival Sloan Digital Sky Survey (SDSS) multi-epoch imaging data (Stripe 82), we have searched for the tidal disruption of stars by supermassive black holes in non-active galaxies. Two candidate tidal disruption events (TDEs) are identified. The TDE flares have optical blackbody temperatures of 2 × 104 K and observed peak luminosities of Mg = -18.3 and -20.4 (νL ν = 5 × 1042, 4 × 10 43 erg s-1, in the rest frame); their cooling rates are very low, qualitatively consistent with expectations for tidal disruption flares. The properties of the TDE candidates are examined using (1) SDSS imaging to compare them to other flares observed in the search, (2) UV emission measured by GALEX, and (3) spectra of the hosts and of one of the flares. Our pipeline excludes optically identifiable AGN hosts, and our variability monitoring over nine years provides strong evidence that these are not flares in hidden AGNs. The spectra and color evolution of the flares are unlike any SN observed to date, their strong late-time UV emission is particularly distinctive, and they are nuclear at high resolution arguing against these being first cases of a previously unobserved class of SNe or more extreme examples of known SN types. Taken together, the observed properties are difficult to reconcile with an SN or an AGN-flare explanation, although an entirely new process specific to the inner few hundred parsecs of non-active galaxies cannot be excluded. Based on our observed rate, we infer that hundreds or thousands of TDEs will be present in current and next-generation optical synoptic surveys. Using the approach outlined here, a TDE candidate sample with O(1) purity can be selected using geometric resolution and host and flare color alone, demonstrating that a campaign to create a large sample of TDEs, with immediate and detailed multi-wavelength follow-up, is feasible. A by-product of this work is quantification of the power spectrum of extreme flares in AGNs. © 2011. The American Astronomical Society. All rights reserved.
• Weisz, D. R., Dalcanton, J. J., Williams, B. F., Gilbert, K. M., Skillman, E. D., Seth, A. C., Dolphin, A. E., B., K., Gogarten, S. M., Holtzman, J., Rosema, K., Cole, A., Karachentsev, I. D., & Zaritsky, D. (2011). The ACS Nearby Galaxy Survey Treasury. VIII. The global star formation histories of 60 dwarf galaxies in the local volume. Astrophysical Journal, 739(1).
  More info

  Abstract: We present uniformly measured star formation histories (SFHs) of 60 nearby (D ≲ 4Mpc) dwarf galaxies based on color-magnitude diagrams of resolved stellar populations from images taken with the Hubble Space Telescope and analyzed as part of the ACS Nearby Galaxy Survey Treasury program (ANGST). This volume-limited sample contains 12 dwarf spheroidal (dSph)/dwarf elliptical (dE), 5 dwarf spiral, 28 dwarf irregular (dI), 12 dSph/dI (transition), and 3 tidal dwarf galaxies. The sample spans a range of ∼10mag in MB and covers a wide range of environments, from highly interacting to truly isolated. From the best-fit SFHs, we find three significant results for dwarf galaxies in the ANGST volume: (1) the majority of dwarf galaxies formed the bulk of their mass prior to z ∼1, regardless of current morphological type; (2) the mean SFHs of dIs, transition dwarf galaxies (dTrans), and dSphs are similar over most of cosmic time, and only begin to diverge a fewGyr ago, with the clearest differences between the three appearing during the most recent 1Gyr; and (3) the SFHs are complex and the mean values are inconsistent with simple SFH models, e.g., single bursts, constant star formation rates (SFRs), or smooth, exponentially declining SFRs. The mean SFHs show clear divergence from the cosmic SFH at z ≲ 0.7, which could be evidence that low-mass systems have experienced delayed star formation relative to more massive galaxies. The sample shows a strong density-morphology relationship, such that the dSphs in the sample are less isolated than the dIs. We find that the transition from a gas-rich to gas-poor galaxy cannot be solely due to internal mechanisms such as stellar feedback, and instead is likely the result of external mechanisms, e.g., ram pressure and tidal stripping and tidal forces. In terms of their environments, SFHs, and gas fractions, the majority of the dTrans appear to be low-mass dIs that simply lack Hα emission, similar to Local Group (LG) dTrans DDO 210. However, a handful of dTrans have remarkably low gas fractions, suggesting that they have nearly exhausted their gas supply, analogous to LG dTrans such as Phoenix. Finally, we have also included extensive exploration of uncertainties in the SFH recovery method, including the optimization of time resolution, the effects of photometric depth, and impact of systematic uncertainties due to the limitations in current stellar evolution models. © 2011. The American Astronomical Society. All rights reserved.
• Weisz, D. R., Dolphin, A. E., Dalcanton, J. J., Skillman, E. D., Holtzman, J., Williams, B. F., Gilbert, K. M., Seth, A. C., Cole, A., Gogarten, S. M., Rosema, K., Karachentsev, I. D., McQuinn, K. B., & Zaritsky, D. (2011). How typical are the local group dwarf galaxies?. Astrophysical Journal, 743(1).
  More info

  Abstract: We compare the cumulative star formation histories (SFHs) of Local Group (LG) dwarf galaxies with those in the volume-limited ACS Nearby Galaxy Survey Treasury (ANGST) sample (D ≲ 4Mpc), in order to understand how typical the LG dwarf galaxies are relative to those in the nearby universe. The SFHs were derived in a uniform manner from high-quality optical color-magnitude diagrams constructed from Hubble Space Telescope imaging. We find that the mean cumulative SFHs of the LG dwarfs are comparable to the mean cumulative SFHs of the ANGST sample for the three different morphological types (dwarf spheroidals/ellipticals: dSph/dE; dwarf irregulars: dI; transition dwarfs: dTrans). We also discuss effects such as population gradients and systematic uncertainties in the stellar models that may influence the derived SFHs. Both the ANGST and LG dwarf galaxies show a consistent and strong morphology-density relationship, emphasizing the importance of environment in the evolution of dwarf galaxies. Specifically, we confirm that dIs are found at lower densities and higher luminosities than dSphs, within this large sample. We also find that dTrans are located in similar environments to those occupied by dwarf irregular galaxies, but have systematically lower luminosities that are more comparable to those of dwarf spheroidals. The similarity of the SFHs and morphology-density relationships of the LG and ANGST dwarf galaxies suggests that the LG dwarfs are a good representation of dwarf galaxies in the local universe. © 2011. The American Astronomical Society. All rights reserved.
• Weisz, D. R., Dolphin, A. E., Dalcanton, J. J., Skillman, E. D., Holtzman, J., Williams, B. F., Gilbert, K. M., Seth, A. C., Cole, A., Gogarten, S. M., Rosema, K., Karachentsev, I. D., McQuinn, K., & Zaritsky, D. (2011). HOW TYPICAL ARE THE LOCAL GROUP DWARF GALAXIES?. ASTROPHYSICAL JOURNAL, 743(1).
• Werchan, F., & Zaritsky, D. (2011). THE STAR CLUSTERS OF THE LARGE MAGELLANIC CLOUD: STRUCTURAL PARAMETERS. ASTRONOMICAL JOURNAL, 142(2).
• Werchan, F., & Zaritsky, D. (2011). The star clusters of the large magellanic cloud: Structural parameters. Astronomical Journal, 142(2).
  More info

  Abstract: We present and analyze the radial luminosity profiles of a sample of 1066 stellar clusters in the Large Magellanic Cloud (LMC). By design, this study closely follows the compilation by Hill & Zaritsky of the structural parameters of stellar clusters in the Small Magellanic Cloud (SMC). Both King and Elson-Fall-Freeman model profiles are fit to V-band surface brightness profiles measured from the Magellanic Cloud Photometric Survey images. We tabulate the concentration, central surface brightness, tidal radii, 90% enclosed luminosity radii (r 90), and local background luminosity density. Over two-thirds of the clusters in the sample are adequately fit by one or both of these models. One notable and systematic exception, as in the SMC, is those clusters that lack a central brightness concentration, the "ring" clusters. While the bulk properties of the clusters are similar between the LMC and SMC populations, we find that the LMC lacks clusters that are as large, either in terms of core radii or r 90, as the largest in the SMC, perhaps a signature of larger tidal stresses in the LMC. © 2011. The American Astronomical Society. All rights reserved..
• Yang, Y., Zabludoff, A., Zaritsky, D., Lauer, T., & Mihos, J. (2011). E=A galaxies and the formation of early-type galaxies at z similar to 0. ASTROPHYSICAL JOURNAL, 607(1), 258-273.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2011). Star Clusters, Galaxies, and the Fundamental Manifold. The Astrophysical Journal, 727(2), 116. doi:10.1088/0004-637x/727/2/116
  More info

  We explore whether global observed properties, specifically half-light radii, mean surface brightness, and integrated stellar kinematics, suffice to unambiguously differentiate galaxies from star clusters, which presumably formed differently and lack dark matter halos. We find that star clusters lie on the galaxy scaling relationship referred to as the fundamental manifold (FM), on the extension of a sequence of compact galaxies, and so conclude that there is no simple way to differentiate star clusters from ultracompact galaxies. By extending the validity of the FM over a larger range of parameter space and a wider set of objects, we demonstrate that the physics that constrains the resulting baryon and dark matter distributions in stellar systems is more general than previously appreciated. The generality of the FM implies (1) that the stellar spatial distribution and kinematics of one type of stellar system do not arise solely from a process particular to that set of systems, such as violent relaxation for elliptical galaxies, but are instead the result of an interplay of all processes responsible for the generic settling of baryons in gravitational potential wells, (2) that the physics of how baryons settle is independent of whether the system is embedded within a dark matter halo, and (3) that peculiar initial conditions at formation or stochastic events during evolution do not ultimately disturb the overall regularity of baryonic settling. We also utilize the relatively simple nature of star clusters to relate deviations from the FM to the age of the stellar population and find that stellar population models systematically and significantly overpredict the mass-to-light ratios of old, metal-rich clusters. We present an empirical calibration of stellar population mass-to-light ratios with age and color. Finally, we use the FM to estimate velocity dispersions for the low surface brightness, outer halo clusters that lack such measurements.
• Zaritsky, D. (2011). Astrophysical Tests of the Nature of Dark Matter, the Expansion of the Universe, and Evolving Physical Constants. Bulletin of the American Physical Society, 2011.
• Zaritsky, D., Williams, B. F., Weisz, D. R., Skillman, E. D., Seth, A. C., Rosema, K., Mcquinn, K. B., Karachentsev, I. D., Holtzman, J., Gogarten, S. M., Gilbert, K. M., Dolphin, A. E., Dalcanton, J. J., & Cole, A. A. (2011). THE ACS NEARBY GALAXY SURVEY TREASURY. VIII. THE GLOBAL STAR FORMATION HISTORIES OF 60 DWARF GALAXIES IN THE LOCAL VOLUME. The Astrophysical Journal, 739(1), 5. doi:10.1088/0004-637x/739/1/5
  More info

  We present uniformly measured star formation histories (SFHs) of 60 nearby (D less than or similar to 4 Mpc) dwarf galaxies based on color-magnitude diagrams of resolved stellar populations from images taken with the Hubble Space Telescope and analyzed as part of the ACS Nearby Galaxy Survey Treasury program (ANGST). This volume-limited sample contains 12 dwarf spheroidal (dSph)/dwarf elliptical (dE), 5 dwarf spiral, 28 dwarf irregular (dI), 12 dSph/dI (transition), and 3 tidal dwarf galaxies. The sample spans a range of similar to 10 mag in MB and covers a wide range of environments, from highly interacting to truly isolated. From the best-fit SFHs, we find three significant results for dwarf galaxies in the ANGST volume: (1) the majority of dwarf galaxies formed the bulk of their mass prior to z similar to 1, regardless of current morphological type; (2) the mean SFHs of dIs, transition dwarf galaxies (dTrans), and dSphs are similar over most of cosmic time, and only begin to diverge a few Gyr ago, with the clearest differences between the three appearing during the most recent 1 Gyr; and (3) the SFHs are complex and the mean values are inconsistent with simple SFH models, e. g., single bursts, constant star formation rates (SFRs), or smooth, exponentially declining SFRs. The mean SFHs show clear divergence from the cosmic SFH at z less than or similar to 0.7, which could be evidence that low-mass systems have experienced delayed star formation relative to more massive galaxies. The sample shows a strong density-morphology relationship, such that the dSphs in the sample are less isolated than the dIs. We find that the transition from a gas-rich to gas-poor galaxy cannot be solely due to internal mechanisms such as stellar feedback, and instead is likely the result of external mechanisms, e. g., ram pressure and tidal stripping and tidal forces. In terms of their environments, SFHs, and gas fractions, the majority of the dTrans appear to be low-mass dIs that simply lack Ha emission, similar to Local Group (LG) dTrans DDO 210. However, a handful of dTrans have remarkably low gas fractions, suggesting that they have nearly exhausted their gas supply, analogous to LG dTrans such as Phoenix. Finally, we have also included extensive exploration of uncertainties in the SFH recovery method, including the optimization of time resolution, the effects of photometric depth, and impact of systematic uncertainties due to the limitations in current stellar evolution models.
• Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2011). STAR CLUSTERS, GALAXIES, AND THE FUNDAMENTAL MANIFOLD. ASTROPHYSICAL JOURNAL, 727(2).
• Christlein, D., Zaritsky, D., & Bland-Hawthorn, J. (2010). A spectroscopic study of the H alpha surface brightness profiles in the outer discs of galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 405(4), 2549-2560.
• Christlein, D., Zaritsky, D., & Bland-Hawthorn, J. (2010). A spectroscopic study of the Hα surface brightness profiles in the outer discs of galaxies. Monthly Notices of the Royal Astronomical Society, 405(4), 2549-2560.
  More info

  Abstract: The surface brightness profile of Hα emission in galaxies is generally thought to be confined by a sharp truncation, sometimes speculated to coincide with a star formation threshold. Over the past years, observational evidence for both old and young stellar populations, as well as individual H ii regions, has demonstrated that the outer disc is an actively evolving part of a galaxy. To provide constraints on the origin of the aforementioned Hα truncation and the relation of Hα emission in the outer disc to the underlying stellar population, we measure the shape of the outer Hα surface brightness profile of 15 isolated, edge-on late-type disc galaxies using deep, long-slit spectroscopy. Tracing Hα emission up to 50 per cent beyond the optical radius, R25, we find a composite Hα surface brightness profile, well described by a broken-exponential law, that drops more steeply in the outer disc, but which is not truncated. The stellar continuum and Hα surface brightness both exhibit a break at ∼ 0.7 R25, but the Hα emission drops more steeply than the stellar continuum beyond that break. Although profiles with truncations or single exponential laws correctly describe the Hα surface brightness profiles of some individual galaxies, flexible broken exponentials are required in most cases and are therefore the more appropriate generic description. The common existence of a significant second surface brightness component beyond the Hα break radius disfavours the hypothesis that this break is a purely stochastic effect. © 2010 The Authors. Journal compilation © 2010 RAS.
• Chung, S. M., Gonzalez, A. H., Clowe, D., Markevitch, M., & Zaritsky, D. (2010). STAR FORMATION IN THE BULLET CLUSTER. I. THE INFRARED LUMINOSITY FUNCTION AND STAR FORMATION RATE. ASTROPHYSICAL JOURNAL, 725(2), 1536-1549.
• Chung, S. M., Gonzalez, A. H., Clowe, D., Markevitch, M., & Zaritsky, D. (2010). Star formation in the Bullet Cluster. I. the infrared luminosity function and star formation rate. Astrophysical Journal Letters, 725(2), 1536-1549.
  More info

  Abstract: The Bullet Cluster is a massive galaxy cluster at z = 0.297 undergoing a major supersonic (Mach 3) merger event. Using data from Spitzer MIPS and the Infrared Array Camera, optical imaging, and optical spectroscopy, we present the global star formation rate (SFR) of this unique cluster. Using a 90% spectroscopically complete sample of 37 star-forming MIPS confirmed cluster members out to R > 1.7 Mpc, and the Rieke et al. relation to convert from 24 μm flux to SFR, we calculate an integrated obscured SFR of 267M ⊙ yr-1 and a specific SFR of 28M⊙ yr-1 per 1014M⊙. The clustermass normalized integrated SFR of the Bullet Cluster is among the highest in a sample of eight other clusters and cluster mergers from the literature. Five LIRGs and one ULIRG contribute 30% and 40% of the total SFR of the cluster, respectively. To investigate the origin of the elevated specific SFR, we compare the infrared luminosity function (IR LF) of the Bullet Cluster to those of Coma (evolved to z = 0.297) and CL1358+62. The Bullet Cluster IR LF exhibits an excess of sources compared to the IR LFs of the other massive clusters. A Schechter function fit of the Bullet Cluster IR LF yields L * = 44.68±0.11 erg s -1, which is ∼0.25 and 0.35 dex brighter than L * of evolved Coma and CL1358+62, respectively. The elevated IR LF of the Bullet Cluster relative to other clusters can be explained if we attribute the "excess" star-forming IR galaxies to a population associated with the infalling group that has not yet been transformed into quiescent galaxies. In this case, the timescale required for quenching star formation in the cluster environment must be longer than the timescale since the group's accretion-a few hundred million years.We suggest that "strangulation" is likely to be an important process in the evolution of star formation in clusters. © 2010. The American Astronomical Society. All rights reserved.
• Finn, R. A., Desai, V., Rudnick, G., Poggianti, B., Bell, E. F., Hinz, J., Jablonka, P., Milvang-Jensen, B., Moustakas, J., Rines, K., & Zaritsky, D. (2010). DUST-OBSCURED STAR FORMATION IN INTERMEDIATE REDSHIFT GALAXY CLUSTERS. ASTROPHYSICAL JOURNAL, 720(1), 87-98.
• Finn, R. A., Desai, V., Rudnick, G., Poggianti, B., Bell, E. F., Hinz, J., Jablonka, P., Milvang-Jensen, B., Moustakas, J., Rines, K., & Zaritsky, D. (2010). Dust-obscured star formation in intermediate redshift galaxy clusters. Astrophysical Journal Letters, 720(1), 87-98.
  More info

  Abstract: We present Spitzer MIPS 24 μm observations of sixteen 0.4 < z < 0.8 galaxy clusters drawn from the ESO Distant Cluster Survey. This is the first large 24 μm survey of clusters at intermediate redshift. The depth of our imaging corresponds to a total IR luminosity of 8 × 1010 L ⊙, just below the luminosity of luminous infrared galaxies (LIRGs), and 6+1-1% of MV < - 19 cluster members show 24 μm emission at or above this level. We compare with a large sample of coeval field galaxies and find that while the fraction of cluster LIRGs lies significantly below that of the field, the IR luminosities of the field and cluster galaxies are consistent. However, the stellar masses of the EDisCS LIRGs are systematically higher than those of the field LIRGs. A comparison with optical data reveals that ∼80% of cluster LIRGs are blue and the remaining 20% lie on the red sequence. Of LIRGs with optical spectra, 88-4-5% show [O II] emission with EW([O II]) > 5 Å, and ∼75% exhibit optical signatures of dusty starbursts. On average, the fraction of cluster LIRGs increases with projected clustercentric radius but remains systematically lower than the field fraction over the area probed (
• Harris, J., & Zaritsky, D. (2010). The star formation history of the Small Magellanic Cloud. ASTRONOMICAL JOURNAL, 127(3), 1531-1544.
• Herbert-Fort, S., Zaritsky, D., Christlein, D., & Kannappan, S. J. (2010). THE SURFACE MASS DENSITY AND STRUCTURE OF THE OUTER DISK OF NGC 628. ASTROPHYSICAL JOURNAL, 715(2), 902-907.
• Herbert-Fort, S., Zaritsky, D., Christlein, D., & Kannappan, S. J. (2010). The surface mass density and structure of the outer disk of NGC 628. Astrophysical Journal Letters, 715(2), 902-907.
  More info

  Abstract: We study the kinematics of GALEX-selected Hα knots in the outer disk (beyond R 25) of NGC 628 (M74), a galaxy representative of large, undisturbed, extended UV (type 1 XUV) disks. Our spectroscopic target sample of 235 of the bluest UV knots surrounding NGC 628 yielded 15 Hα detections (6%), roughly the number expected given the different mean ages of the two populations. The measured vertical velocity dispersion of the Hα knots between 1and1.8 R 25 (13.5-23.2 kpc) is
• Just, D. W., Zaritsky, D., Sand, D. J., Desai, V., & Rudnick, G. (2010). THE ENVIRONMENTAL DEPENDENCE OF THE EVOLVING S0 FRACTION. ASTROPHYSICAL JOURNAL, 711(1), 192-200.
• Just, D. W., Zaritsky, D., Sand, D. J., Desai, V., & Rudnick, G. (2010). The environmental dependence of the evolving S0 fraction. Astrophysical Journal Letters, 711(1), 192-200.
  More info

  Abstract: We re-investigate the dramatic rise in the S0 fraction, f S0, within clusters since z ∼ 0.5. In particular, we focus on the role of the global galaxy environment on f S0 by compiling, either from our own observations or the literature, robust line-of-sight velocity dispersions, σ′s, for a sample of galaxy groups and clusters at 0.1 < z < 0.8 that have uniformly determined, published morphological fractions. We find that the trend of f S0 with redshift is twice as strong for σ < 750 km s-1 groups/poor clusters than for higher-σ, rich clusters. From this result, we infer that over this redshift range galaxy-galaxy interactions, which are more effective in lower-σ environments, are more responsible for transforming spiral galaxies into S0's than galaxy-environment processes, which are more effective in higher-σ environments. The rapid, recent growth of the S0 population in groups and poor clusters implies that large numbers of progenitors exist in low-σ systems at modest redshifts (0.5), where morphologies and internal kinematics are within the measurement range of current technology. © 2010 The American Astronomical Society.
• Saglia, R. P., Sanchez-Blazquez, P., Bender, R., Simard, L., Desai, V., Aragon-Salamanca, A., Milvang-Jensen, B., Halliday, C., Jablonka, P., Noll, S., Poggianti, B., Clowe, D. I., De, L. G., Pello, R., Rudnick, G., Valentinuzzi, T., White, S., & Zaritsky, D. (2010). The fundamental plane of EDisCS galaxies The effect of size evolution. ASTRONOMY & ASTROPHYSICS, 524.
• Saglia, R. P., Sánchez-Blázquez, P., Bender, R., Simard, L., Desai, V., Aragón-Salamanca, A., Milvang-Jensen, B., Halliday, C., Jablonka, P., Noll, S., Poggianti, B., Clowe, D. I., Lucia, G. D., Pelló, R., Rudnick, G., Valentinuzzi, T., White, S. D., & Zaritsky, D. (2010). The fundamental plane of EDisCS galaxies: The effect of size evolution. Astronomy and Astrophysics, 524(1).
  More info

  Abstract: We study the evolution of spectral early-type galaxies in clusters, groups, and the field up to redshift 0.9 using the ESO Distant Cluster Survey (EDisCS) dataset. We measure structural parameters (circularized half-luminosity radii Re, surface brightness Ie, and velocity dispersions s) for 154 cluster and 68 field galaxies. On average, we achieve precisions of 10% in Re, 0.1 dex in logIe, and 10% in s. We sample ≈20% of cluster and ≈10% of field spectral early-type galaxies to an I band magnitude in a 1 arcsec radius aperture as faint as I1 = 22. We study the evolution of the zero point of the fundamental plane (FP) and confirm results in the literature, but now also for the low cluster velocity dispersion regime. Taken at face value, the mass-to-light ratio varies as δlog M/LB = (-0.54 ± 0.01)z = (-1.61 ± 0.01) log(1 + z) in clusters, independent of their velocity dispersion. The evolution is stronger (δlog M/LB = (-0.76 ± 0.01)z = (-2.27 ± 0.03) log(1 + z)) for field galaxies. A somewhat milder evolution is derived if a correction for incompleteness is applied. A rotation in the FP with redshift is detected with low statistical significance. The a and ß FP coefficients decrease with redshift, or, equivalently, the FP residuals correlate with galaxy mass and become progressively negative at low masses. The effect is visible at z = 0.7 for cluster galaxies and at lower redshifts z = 0.5 for field galaxies. We investigate the size evolution of our galaxy sample. In agreement with previous results, we find that the half-luminosity radius for a galaxy with a dynamical or stellar mass of 2 × 1011 M varies as (1 + z)-1.0±0.3 for both cluster and field galaxies. At the same time, stellar velocity dispersions grow with redshift, as (1 + z)0.59±0.10 at constant dynamical mass, and as (1 + z)0.34±0.14 at constant stellar mass. The measured size evolution reduces to Re . (1 + z)-0.5±0.2 and s . (1 + z)0.41±0.08, at fixed dynamical masses, and Re . (1 + z)-0.68±0.4 and s . (1 + z)0.19±0.10, at fixed stellar masses, when the progenitor bias (PB, galaxies that locally are of spectroscopic early-type, but are not very old, disappear progressively from the EDisCS high-redshift sample; often these galaxies happen to be large in size) is taken into account. Taken together, the variations in size and velocity dispersion imply that the luminosity evolution with redshift derived from the zero point of the FP is somewhat milder than that derived without taking these variations into account. When considering dynamical masses, the effects of size and velocity dispersion variations almost cancel out. For stellar masses, the luminosity evolution is reduced to LB . (1+ z)1.0 for cluster galaxies and LB . (1+ z)1.67 for field galaxies. Using simple stellar population models to translate the observed luminosity evolution into a formation age, we find that massive (≤1011 M) cluster galaxies are old (with a formation redshift zf ≥ 1.5) and lower mass galaxies are 3-4 Gyr younger, in agreement with previous EDisCS results from color and line index analyses. This confirms the picture of a progressive build-up of the red sequence in clusters with time. Field galaxies follow the same trend, but are ≈1 Gyr younger at a given redshift and mass. Taking into account the size and velocity dispersion evolution quoted above pushes all formation ages upwards by 1 to 4 Gyr. © ESO, 2010.
• Sand, D. J., Seth, A., Olszewski, E. W., Willman, B., Zaritsky, D., & Kallivayalil, N. (2010). A DEEPER LOOK AT LEO IV: STAR FORMATION HISTORY AND EXTENDED STRUCTURE. ASTROPHYSICAL JOURNAL, 718(1), 530-542.
• Sheth, K., Regan, M., Hinz, J. L., Gil, A., Menéndez-Delmestre, K., Muñoz-Mateos, J., Seibert, M., Kim, T., Laurikainen, E., Salo, H., Gadotti, D. A., Laine, J., Mizusawa, T., Armus, L., Athanassoula, E., Bosma, A., Buta, R. J., Capak, P., Jarrett, T. H., , Elmegreen, D. M., et al. (2010). The Spitzer Survey of Stellar Structure in Galaxies (S⁴G). Publications of the Astronomical Society of the Pacific, 122(898), 1397-1414.
  More info

  Abstract: The Spitzer Survey of Stellar Structure in Galaxies (S4G) is an Exploration Science Legacy Program approved for the Spitzer post-cryogenic mission. It is a volume-, magnitude-, and size-limited (d > 40 Mpc, |b| > 30°, mBcorr < 15:5, and D25 > 1′) survey of 2331 galaxies using the Infrared Array Camera (IRAC) at 3.6 and 4.5 μm. Each galaxy is observed for 240 s and mapped to ≥1:5 × D25. The final mosaicked images have a typical 1σ rms noise level of 0.0072 and 0:0093 MJy sr-1 at 3.6 and 4.5 μm, respectively. Our azimuthally averaged surface brightness profile typically traces isophotes at μ36μm(AB)(1σ) ∼ 27 magarcsec-2, equivalent to a stellar mass surface density of ∼1 Ṁpc-2. S4G thus provides an unprecedented data set for the study of the distribution of mass and stellar structures in the local universe. This large, unbiased, and extremely deep sample of all Hubble types from dwarfs to spirals to ellipticals will allow for detailed structural studies, not only as a function of stellar mass, but also as a function of the local environment. The data from this survey will serve as a vital testbed for cosmological simulations predicting the stellar mass properties of present-day galaxies. This article introduces the survey and describes the sample selection, the significance of the 3.6 and 4.5 μm bands for this study, and the data collection and survey strategies. We describe the S4G data analysis pipeline and present measurements for a first set of galaxies, observed in both the cryogenic and warm mission phases of Spitzer. For every galaxy we tabulate the galaxy diameter, position angle, axial ratio, inclination at μ36μm(AB) = 25:5, and 26:5 mag arcsec-2 (equivalent to ≈μ B(AB) = 27:2 and 28:2 magarcsec-2, respectively). These measurements will form the initial S4G catalog of galaxy properties. We also measure the total magnitude and the azimuthally averaged radial profiles of ellipticity, position angle, surface brightness, and color. Finally, using the galaxy-fitting code GALFIT, we deconstruct each galaxy into its main constituent stellar components: the bulge/spheroid, disk, bar, and nuclear point source, where necessary. Together, these data products will provide a comprehensive and definitive catalog of stellar structures, mass, and properties of galaxies in the nearby universe and will enable a variety of scientific investigations, some of which are highlighted in this introductory S 4G survey paper. © 2010. The Astronomical Society of the Pacific.
• Zaritsky, D., & Psaltis, D. (2010). OUTER GALACTIC DISKS AND A QUANTITATIVE TEST OF GRAVITY AT LOW ACCELERATIONS. ASTROPHYSICAL JOURNAL LETTERS, 720(1), L11-L14.
• Zaritsky, D., & Psaltis, D. (2010). Outer galactic disks and a quantitative test of gravity at low accelerations. Astrophysical Journal Letters, 720(1 PART 2), L11-L14.
  More info

  Abstract: We use the recent measurement of the velocity dispersion of star-forming, outer-disk knots by Herbert-Fort et al. in the nearly face-on galaxy NGC 628, in combination with other data from the literature, to execute a straightforward test of gravity at low accelerations. Specifically, the rotation curve at large radius sets the degree of non-standard acceleration and then the predicted scale height of the knots at that radius provides the test of the scenario. For our demonstration, we presume that the Hα knots, which are young (age < 10 Myr), are distributed like the gas from which they have recently formed and find a marginal (>97% confidence) discrepancy with a modified gravity scenario given the current data. More interestingly, we demonstrate that there is no inherent limitation that prevents such a test from reaching possible discrimination at the >4σ level with a reasonable investment of observational resources. © 2010. The American Astronomical Society. All rights reserved.
• Badenes, C., Harris, J., Zaritsky, D., & Prieto, J. L. (2009). Star formation around the youngest supernova remnants in the large magellanic cloud: Implications for type la supernova progenitors. AIP Conference Proceedings, 1111, 615-617.
  More info

  Abstract: We use the star formation history map of the Large Magellanic Cloud recently published by Harris & Zaritsky to study the sites of the four smallest (and presumably youngest) Type la supernova remnants: 0509-67.5, 0519-69.0, N103B and DEM L71. We find that three of the four Type la remnants are associated with old, metal-poor stellar populations, with little or no recent star formation. These include SNR 0509-67.5 which is known to have been originated by an extremely bright SN 1991 T-like event, and yet is located very far away from any star forming regions. It is very unlikely that this bright Type la SN had a young stellar progenitor The fourth Type la remnant, SNR N103B is associated with vigorous star formation activity in the last 100 Myr, and might have had a relatively younger and more massive progenitor. © 2009 American Institute of Physics.
• Badenes, C., Harris, J., Zaritsky, D., & Prieto, J. L. (2009). THE STELLAR ANCESTRY OF SUPERNOVAE IN THE MAGELLANIC CLOUDS. I. THE MOST RECENT SUPERNOVAE IN THE LARGE MAGELLANIC CLOUD. ASTROPHYSICAL JOURNAL, 700(1), 727-740.
• Barazza, F. D., Jablonka, P., Desai, V., Jogee, S., Aragón-Salamanca, A., Lucia, G. D., Saglia, R. P., Halliday, C., Poggianti, B. M., Dalcanton, J. J., Rudnick, G., Milvang-Jensen, B., Noll, S., Simard, L., Clowe, D. I., Pelló, R., White, S. D., & Zaritsky, D. (2009). Frequency and properties of bars in cluster and field galaxies at intermediate redshifts. Astronomy and Astrophysics, 497(3), 713-728.
  More info

  Abstract: We present a study of large-scale bars in field and cluster environments out to redshifts of ∼0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The properties of bars and disks are determined by ellipse fits to the surface brightness distribution of the galaxies using HST/ACS images in the F814W filter. The bar identification is based on quantitative criteria after highly inclined (> 60o) systems have been excluded. The total optical bar fraction in the redshift range (median z = 0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (∼31%) than at larger distances (∼18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (∼45%) than bulge-dominated galaxies (∼15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. The question whether internal or external factors are more important for bar formation and evolution cannot be answered definitely. On the one hand, the bar fraction and properties of cluster and field samples of disk galaxies are quite similar, indicating that internal processes are crucial for bar formation. On the other hand, we find evidence that cluster centers are favorable locations for bars, which suggests that the internal processes responsible for bar growth are supported by the typical interactions taking place in such environments. © 2009 ESO.
• Blum, R. D., Mould, J. R., Olsen, K. A., Frogel, J. A., Werner, M., Meixner, M., Markwick-Kemper, F., Indebetouw, R., Whitney, B., Meade, M., Babler, B., Churchwell, E. B., Gordon, K., Engelbracht, C., For, B. -., Misselt, K., Vijh, U., Leitherer, C., Volk, K., , Points, S., et al. (2009). Spitzer sage survey of the large magellanic cloud. II. Evolved stars and infrared color-magnitude diagrams. ASTRONOMICAL JOURNAL, 132(5), 2034-2045.
• Bradac, M., Treu, T., Applegate, D., Gonzalez, A. H., Clowe, D., Forman, W., Jones, C., Marshall, P., Schneider, P., & Zaritsky, D. (2009). FOCUSING COSMIC TELESCOPES: EXPLORING REDSHIFT z similar to 5-6 GALAXIES WITH THE BULLET CLUSTER 1E0657-56. ASTROPHYSICAL JOURNAL, 706(2), 1201-1212.
• Bradač, M., Treu, T., Applegate, D., Gonzalez, A. H., Clowe, D., Forman, W., Jones, C., Marshall, P., Schneider, P., & Zaritsky, D. (2009). Focusing cosmic telescopes: Exploring redshift z 5-6 galaxies with the bullet cluster 1E0657 56. Astrophysical Journal Letters, 706(2), 1201-1212.
  More info

  Abstract: The gravitational potential of clusters of galaxies acts as a cosmic telescope allowing us to find and study galaxies at fainter limits than otherwise possible and thus probe closer to the epoch of formation of the first galaxies. We use the Bullet cluster 1E0657 - 56 (z = 0.296) as a case study, because its high mass and merging configuration makes it one of the most efficient cosmic telescopes we know. We develop a new algorithm to reconstruct the gravitational potential of the Bullet cluster based on a non-uniform adaptive grid, combining strong and weak gravitational lensing data derived from deep Hubble Space Telescope/Advanced Camera for Surveys F606W-F775W-F850LP and ground-based imaging. We exploit this improved mass map to study z ∼ 5-6 Lyman break galaxies (LBGs), which we detect as dropouts. One of the LBGs is multiply imaged, providing a geometric confirmation of its high redshift, and is used to further improve our mass model. We quantify the uncertainties in the magnification map reconstruction in the intrinsic source luminosity, and in the volume surveyed, and show that they are negligible compared to sample variance when determining the luminosity function of high-redshift galaxies. With shallower and comparable magnitude limits to Hubble Ultra Deep Field (HUDF) and Great Observatories Origins Deep Survey (GOODS), the Bullet cluster observations, after correcting for magnification, probe deeper into the luminosity function of the high-redshift galaxies than GOODS and only slightly shallower than HUDF. We conclude that accurately focused cosmic telescopes are the most efficient way to sample the bright end of the luminosity function of high-redshift galaxies and - in case they are multiply imaged - confirm their redshifts. © 2009. The American Astronomical Society. All rights reserved.
• Brown, M., Moustakas, J., Caldwell, N., Palamara, D., Cool, R. J., Dey, A., Hickox, R. C., Jannuzi, B. T., Murray, S. S., & Zaritsky, D. (2009). ACTIVE GALACTIC NUCLEI AND THE TRUNCATION OF STAR FORMATION IN K plus A GALAXIES. ASTROPHYSICAL JOURNAL, 703(1), 150-158.
• Chung, S. M., Gonzalez, A. H., Clowe, D., Zaritsky, D., Markevitch, M., & Jones, C. (2009). IMPACTS OF A SUPERSONIC SHOCK FRONT ON STAR FORMATION IN THE BULLET CLUSTER. ASTROPHYSICAL JOURNAL, 691(2), 963-970.
• Chung, S. M., Gonzalez, A. H., Clowe, D., Zaritsky, D., Markevitch, M., & Jones, C. (2009). Impacts of a supersonic shock front on star formation in the Bullet Cluster. Astrophysical Journal, 691(2), 963-970.
  More info

  Abstract: We use the Bullet Cluster (1E0657-56) to investigate the extent to which star formation in cluster galaxies is influenced by ram pressure from supersonic gas (Mach 3) during a cluster merger. While the effects of ram pressure have been studied for individual galaxies infalling into galaxy clusters, this system provides a unique opportunity to investigate the impact of dramatic merger events on the cluster galaxy population. In this analysis, we use Spitzer IRAC data to study star formation. At the redshift of the cluster, the 6.2 μm PAH feature is redshifted into the 8 μm band, enabling use of the m 4.5-m 8 color as a proxy for specific star formation rate. We find that the color distribution on the two sides of the shock differs by less than 2σ, and conclude that ram pressure from the shock front has no dramatic, immediate impact on the star formation of cluster galaxies in the Bullet Cluster. © 2009. The American Astronomical Society. All rights reserved..
• Dalcanton, J. J., Williams, B. F., Seth, A. C., Dolphin, A., Holtzman, J., Rosema, K., Skillman, E. D., Cole, A., Girardi, L., Gogarten, S. M., Karachentsev, I. D., Olsen, K., Weisz, D., Christensen, C., Freeman, K., Gilbert, K., Gallart, C., Harris, J., Hodge, P., , S., R., et al. (2009). The acs nearby galaxy survey treasury. Astrophysical Journal, Supplement Series, 183(1), 67-108.
  More info

  Abstract: The ACS Nearby Galaxy Survey Treasury (ANGST) is a systematic survey to establish a legacy of uniform multi-color photometry of resolved stars for a volume-limited sample of nearby galaxies (D < 4 Mpc). The survey volume encompasses 69 galaxies in diverse environments, including close pairs, small and large groups, filaments, and truly isolated regions. The galaxies include a nearly complete range of morphological types spanning a factor of 104 in luminosity and star formation rate. The survey data consist of images taken with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST), supplemented with archival data and new Wide Field Planetary Camera 2 (WFPC2) imaging taken after the failure of ACS. Survey images include wide field tilings covering the full radial extent of each galaxy, and single deep pointings in uncrowded regions of the most massive galaxies in the volume. The new wide field imaging in ANGST reaches median 50% completenesses of m F475W = 28.0mag, m F606W = 27.3mag, and m F814W = 27.3mag, several magnitudes below the tip of the red giant branch (TRGB). The deep fields reach magnitudes sufficient to fully resolve the structure in the red clump. The resulting photometric catalogs are publicly accessible and contain over 34 million photometric measurements of >14 million stars. In this paper we present the details of the sample selection, imaging, data reduction, and the resulting photometric catalogs, along with an analysis of the photometric uncertainties (systematic and random), for both ACS and WFPC2 imaging. We also present uniformly derived relative distances measured from the apparent magnitude of the TRGB. © 2009. The American Astronomical Society. All rights reserved.
• De, L. G., Poggianti, B. M., Halliday, C., Milvang-Jensen, B., Noll, S., Smail, I., & Zaritsky, D. (2009). On the role of the post-starburst phase in the buildup of the red sequence of intermediate-redshift clusters. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 400(1), 68-77.
• Gonzalez, A. H., Clowe, D., Bradac, M., Zaritsky, D., Jones, C., & Markevitch, M. (2009). A MULTIPLY IMAGED LUMINOUS INFRARED GALAXY BEHIND THE BULLET CLUSTER (1E0657-56). ASTROPHYSICAL JOURNAL, 691(1), 525-530.
• Gonzalez, A. H., Clowe, D., Bradač, M., Zaritsky, D., Jones, C., & Markevitch, M. (2009). A multiply imaged luminous infrared galaxy behind the bullet cluster (1E0657-56). Astrophysical Journal, 691(1), 525-530.
  More info

  Abstract: We present evidence for a Spitzer-selected luminous infrared galaxy (LIRG) behind the Bullet Cluster (1E0657-56). The galaxy, originally identified as a multiply imaged source using Infrared Array Camera (IRAC) photometry, has a spectral energy distribution consistent with a highly extincted (AV ∼ 3.3), strongly star forming galaxy at z = 2.7. Using our strong gravitational lensing model presented in a previous paper, we find that the magnifications are |μ| ≈ 10-50 for the three images of the galaxy. The brightest and faintest images differ by a factor of 3.2 in magnification. The implied infrared luminosity is consistent with the galaxy being a LIRG, with a stellar mass of M®* ∼ 2 × 1010 M ® and a star formation rate (SFR) of ∼90 M® yr-1. With lensed fluxes at 24 μm of 0.58 mJy and 0.39 mJy in the two brightest images, this galaxy presents a unique opportunity for detailed study of an obscured starburst with a SFR comparable to that of L* galaxies at z > 2. © 2009. The American Astronomical Society. All rights reserved..
• Harris, J., & Zaritsky, D. (2009). The star formation history of the large magellanic cloud. Astronomical Journal, 138(5), 1243-1260.
  More info

  Abstract: We present the first ever global, spatially resolved reconstruction of the star formation history (SFH) of the Large Magellanic Cloud (LMC), based on the application of our StarFISH analysis software to the multiband photometry of 20 million of its stars from the Magellanic Clouds Photometric Survey. The general outlines of our results are consistent with previously published results: following an initial burst of star formation, there was a quiescent epoch from approximately 12 to 5 Gyr ago. Star formation then resumed and has proceeded until the current time at an average rate of roughly 0.2 M ⊙ yr-1, with temporal variations at the factor of 2 level. The re-ignition of star formation about 5 Gyr ago, in both the LMC and Small Magellanic Cloud (SMC), is suggestive of a dramatic event at that time in the Magellanic system. Among the global variations in the recent star formation rate are peaks at roughly 2 Gyr, 500 Myr, 100 Myr, and 12 Myr. The peaks at 500 Myr and 2 Gyr are nearly coincident with similar peaks in the SFH of the SMC, suggesting a joint history for these galaxies extending back at least several Gyr. The chemical enrichment history recovered from our StarFISH analysis is in broad agreement with that inferred from the LMC's star cluster population, although our constraints on the ancient chemical enrichment history are weak. We conclude from the concordance between the star formation and chemical enrichment histories of the field and cluster populations that the field and cluster star formation modes are tightly coupled. © 2009 The American Astronomical Society. All rights reserved.
• Herbert-Fort, S., Zaritsky, D., Moustakas, J., Christlein, D., Wilcots, E., Baruffolo, A., DiPaola, A., Fontana, A., Giallongo, E., Pogge, R. W., Ragazzoni, R., & Smareglia, R. (2009). SPATIALLY CORRELATED CLUSTER POPULATIONS IN THE OUTER DISK OF NGC 3184. ASTROPHYSICAL JOURNAL, 700(2), 1977-1987.
• Herbert-Fort, S., Zaritsky, D., Moustakas, J., Christlein, D., Wilcots, E., Baruffolo, A., Dipaola, A., Fontana, A., Giallongo, E., Pogge, R. W., Ragazzoni, R., & Smareglia, R. (2009). Spatially correlated cluster populations in the outer disk of ngc 3184. Astrophysical Journal Letters, 700(2), 1977-1987.
  More info

  Abstract: We use deep (27.5 mag V-band point-source limiting magnitude) V- and U-band Large Binocular Telescope imaging to study the outer disk (beyond the optical radius R 25) of the non-interacting, face-on spiral galaxy NGC 3184 (D = 11.1 Mpc; R 25 = 11.1 kpc) and find that this outer disk contains >1000 objects (or marginally resolved "knots") resembling star clusters with masses 102-104 M and ages up to 1Gyr. We find statistically significant numbers of these cluster-like knots extending to 1.4 R 25, with the redder knots outnumbering bluer at the largest radii. We measure clustering among knots and find significant correlation to galactocentric radii of 1.5 R 25 for knot separations
• Lee, M. G., Yuk, I., Park, H. S., Harris, J., & Zaritsky, D. (2009). STAR FORMATION HISTORY AND CHEMICAL EVOLUTION OF THE SEXTANS DWARF SPHEROIDAL GALAXY. ASTROPHYSICAL JOURNAL, 703(1), 692-701.
• Lee, M. G., Yuk, I., Park, H. S., Harris, J., & Zaritsky, D. (2009). Star formation history and chemical evolution of the sextans dwarf spheroidal galaxy. Astrophysical Journal Letters, 703(1), 692-701.
  More info

  Abstract: We present the star formation history (SFH) and chemical evolution of the Sextans dSph galaxy as a function of a galactocentric distance. We derive these from the VI photometry of stars in the 42′ × 28′ field using the SMART model developed by Yuk & Lee and adopting a closed-box model for chemical evolution. For the adopted age of Sextans 15 Gyr, we find that >84% of the stars formed prior to 11 Gyr ago, significant star formation extends from 15 to 11 Gyr ago ( 65% of the stars formed 13-15 Gyr ago, while 25% formed 11-13 Gyr ago), detectable star formation continued to at least 8 Gyr ago, the SFH is more extended in the central regions than the outskirts, and the difference in star formation rates between the central and outer regions is most marked 11-13 Gyr ago. Whether blue straggler stars are interpreted as intermediate-age main-sequence stars affects conclusions regarding the SFH for times 4-8 Gyr ago, but this is at most only a trace population. We find that the metallicity of the stars increased rapidly up to [Fe/H] = -1.6 in the central region and to [Fe/H] = -1.8 in the outer region within the first Gyr, and has varied slowly since then. The abundance ratios of several elements derived in this study are in good agreement with the observational data based on the high-resolution spectroscopy in the literature. We conclude that the primary driver for the radial gradient of the stellar population in this galaxy is the SFH, which self-consistently drives the chemical enrichment history. © 2009 The American Astronomical Society. All rights reserved.
• Lucia, G. D., Poggianti, B. M., Halliday, C., Milvang-Jensen, B., Noll, S., Smail, I., & Zaritsky, D. (2009). On the role of the post-starburst phase in the buildup of the red sequence of intermediate-redshift clusters. Monthly Notices of the Royal Astronomical Society, 400(1), 68-77.
  More info

  Abstract: We present new deep spectroscopic observations of 0.05-0.5 L * galaxies in one cluster (cl1232.5-1250) drawn from the ESO (European Southern Observatory) Distant Cluster Survey (EDisCS) sample, at z = 0.54. The new data extend the spectroscopy already available for this cluster by about 1 mag. The cluster has a large fraction of passive galaxies and exhibits a well-defined and relatively tight colour-magnitude relation. Among spectroscopic members, only six galaxies are classified as 'post-starburst' (k+a). For another EDisCS cluster at similar redshift and with as deep spectroscopy, no member is found to have a k+a spectrum. The low measured numbers of post-starburst systems appear to be inadequate to explain the observed increase of faint red galaxies at lower redshift, even when accounting for the infall of new galaxies on to the cluster. Post-starburst galaxies represent a possible channel to move galaxies from the blue star-forming cloud to the red sequence, but the available data suggest this is not the dominant channel in galaxy clusters. If the galaxies at the faint end of the red sequence in nearby clusters originate from the blue galaxies observed in distant galaxy clusters, the transformation must have occurred primarily through physical processes that do not lead to a post-starburst phase. In addition, our data exclude a large population of k+a galaxies at faint magnitudes, as found in the Coma cluster. © 2009 RAS.
• Meidt, S. E., Schinnerer, E., Knapen, J. H., Bosma, A., Athanassoula, E., Sheth, K., Buta, R. J., Zaritsky, D., Laurikainen, E., Elmegreen, D., Elmegreen, B. G., Gadotti, D. A., Salo, H., Regan, M., Ho, L. C., Madore, B. F., Hinz, J. L., Skibba, R. A., Gil de Paz, A., , Munoz-Mateos, J., et al. (2009). RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S(4)G IRAC 3.6 AND 4.5 mu m IMAGES. I. CORRECTING FOR CONTAMINATION BY POLYCYCLIC AROMATIC HYDROCARBONS, HOT DUST, AND INTERMEDIATE-AGE STARS. ASTROPHYSICAL JOURNAL, 744(1).
• Pelló, R., Rudnick, G., Lucia, G. D., Simard, L., Clowe, D. I., Jablonka, P., Milvang-Jensen, B., Saglia, R. P., White, S. D., Aragón-Salamanca, A., Halliday, C., Poggianti, B., Best, P., Dalcanton, J., Dantel-Fort, M., Fort, B., Von, A., Mellier, Y., Rottgering, H., & Zaritsky, D. (2009). Photometric redshifts and cluster tomography in the eso distant cluster survey. Astronomy and Astrophysics, 508(3), 1173-1191.
  More info

  Abstract: Context: This paper reports the results obtained on the photometric redshifts measurement and accuracy, and cluster tomography in the ESO Distant Cluster Survey (EDisCS) fields.Aims: We present the methods used to determine photometric redshifts to discriminate between member and non-member galaxies and reduce the contamination by faint stars in subsequent spectroscopic studies.Methods: Photometric redshifts were computed using two independent codes both based on standard spectral energy distribution (SED) fitting methods (Hyperz and Rudnick's code). Simulations were used to determine the redshift regions for which a reliable determination of photometric redshifts was expected. The accuracy of the photometric redshifts was assessed by comparing our estimates with the spectroscopic redshifts of ̃ 1400 galaxies in the ≤ z ≤ domain. The accuracy expected for galaxies fainter than the spectroscopic control sample was estimated using a degraded version of the photometric catalog for the spectroscopic sample. Results: The accuracy of photometric redshifts is typically σ(δz/(1 + z)) ̃ 0.05 ± 0.01, depending on the field, the filter set, and the spectral type of the galaxies. The quality of the photometric redshifts degrades by a factor of two in σ(δz/(1 + z)) between the brightest (I 90% of all confirmed members.Conclusions. Photometric redshifts are found to be particularly useful for the identification and study of clusters of galaxies in large surveys. They enable efficient and complete pre-selection of cluster members for spectroscopy, allow accurate determinations of the cluster redshifts based on photometry alone, and provide a means of determining cluster membership, especially for bright sources. © 2009 ESO.
• Poggianti, B. M., Aragón-Salamanca, A., Zaritsky, D., Lucia, G. D., Milvang-Jensen, B., Desai, V., Jablonka, P., Halliday, C., Rudnick, G., Varela, J., Bamford, S., Best, P., Clowe, D., Noll, S., Saglia, R., Pelló, R., Simard, L., Von, A., & White, S. (2009). The environments of starburst and post-starburst galaxies at z = 0.4-0.8. Astrophysical Journal, 693(1), 112-131.
  More info

  Abstract: Post-starburst (E+A or k+a) spectra, characterized by their exceptionally strong Balmer lines in absorption and the lack of emission lines, belong to galaxies in which the star formation (SF) activity ended abruptly sometime during the past Gyr. We perform a spectral analysis of galaxies in clusters, groups, poor groups, and the field at z = 0.4-0.8 based on the ESO Distant Cluster Survey. We find that the incidence of k+a galaxies at these redshifts depends strongly on environment. K+a's reside preferentially in clusters and, unexpectedly, in a subset of the σ = 200-400 km s-1 groups, those that have a low fraction of O II emitters. In these environments, 20%-30% of the star-forming galaxies have had their SF activity recently truncated. In contrast, there are proportionally fewer k+a galaxies in the field, the poor groups, and groups with a high O II fraction. An important result is that the incidence of k+a galaxies correlates with the cluster velocity dispersion: more massive clusters have higher proportions of k+a's. Spectra of dusty starburst candidates, with strong Balmer absorption and emission lines, present a very different environmental dependence from k+a's. They are numerous in all environments at z = 0.4-0.8, but they are especially numerous in all types of groups, favoring the hypothesis of triggering by a merger. We present the morphological type, stellar mass, luminosity, mass-to-light ratio, local galaxy density, and clustercentric distance distributions of galaxies of different spectral types. These properties are consistent with previous suggestions that cluster k+a galaxies are observed in a transition phase, at the moment they are rather massive S0 and Sa galaxies, evolving from star-forming, recently infallen later types to passively evolving cluster early-type galaxies. The correlation between k+a fraction and cluster velocity dispersion supports the hypothesis that k+a galaxies in clusters originate from processes related to the intracluster medium, while several possibilities are discussed for the origin of the puzzling k+a frequency in low-O II groups. © 2009. The American Astronomical Society. All rights reserved..
• Rudnick, G., Von, A., Pelló, R., Aragón-Salamanca, A., Marchesini, D., Clowe, D., Lucia, G. D., Halliday, C., Jablonka, P., Milvang-Jensen, B., Poggianti, B., Saglia, R., Simard, L., White, S., & Zaritsky, D. (2009). The rest-frame optical luminosity function of cluster galaxies at z < 0.8 and the assembly of the cluster red sequence. Astrophysical Journal Letters, 700(2), 1559-1588.
  More info

  Abstract: We present the rest-frame optical luminosity function (LF) of red-sequence galaxies in 16 clusters at 0.4 < z < 0.8 drawn from the ESO Distant Cluster Survey (EDisCS). We compare our clusters to an analogous sample from the Sloan Digital Sky Survey (SDSS) and match the EDisCS clusters to their most likely descendants. We measure all LFs down to M ∼ M * + (2.5-3.5). At z < 0.8, the bright end of the LF is consistent with passive evolution but there is a significant buildup of the faint end of the red sequence toward lower redshift. There is a weak dependence of the LF on cluster velocity dispersion for EDisCS but no such dependence for the SDSS clusters. We find tentative evidence that red-sequence galaxies brighter than a threshold magnitude are already in place, and that this threshold evolves to fainter magnitudes toward lower redshifts. We compare the EDisCS LFs with the LF of coeval red-sequence galaxies in the field and find that the bright end of the LFs agree. However, relative to the number of bright red galaxies, the field has more faint red galaxies than clusters at 0.6 < z < 0.8 but fewer at 0.4 < z < 0.6, implying differential evolution. We compare the total light in the EDisCS cluster red sequences to the total red-sequence light in our SDSS cluster sample. Clusters at 0.4 < z < 0.8 must increase their luminosity on the red sequence (and therefore stellar mass in red galaxies) by a factor of 1-3 by z = 0. The necessary processes that add mass to the red sequence in clusters predict local clusters that are overluminous as compared to those observed in the SDSS. The predicted cluster luminosities can be reconciled with observed local cluster luminosities by combining multiple previously known effects. © 2009 The American Astronomical Society. All rights reserved.
• Sanchez-Blazquez, P., Jablonka, P., Noll, S., Poggianti, B. M., Moustakas, J., Milvang-Jensen, B., Halliday, C., Aragon-Salamanca, A., Saglia, R. P., Desai, V., De, L. G., Clowe, D. I., Pello, R., Rudnick, G., Simard, L., White, S., & Zaritsky, D. (2009). Evolution of red-sequence cluster galaxies from redshift 0.8 to 0.4: ages, metallicities, and morphologies. ASTRONOMY & ASTROPHYSICS, 499(1), 47-68.
• Sand, D. J., Olszewski, E. W., Willman, B., Zaritsky, D., Seth, A., Harris, J., Piatek, S., & Saha, A. (2009). THE STAR FORMATION HISTORY AND EXTENDED STRUCTURE OF THE HERCULES MILKY WAY SATELLITE. ASTROPHYSICAL JOURNAL, 704(2), 898-914.
• Simard, L., Clowe, D., Desai, V., Dalcanton, J. J., Von, A., Poggianti, B. M., White, S. D., Aragón-Salamanca, A., Lucia, G. D., Halliday, C., Jablonka, P., Milvang-Jensen, B., Saglia, R. P., Pelló, R., Rudnick, G. H., & Zaritsky, D. (2009). Evolution of the early-type galaxy fraction in clusters since z = 0.8. Astronomy and Astrophysics, 508(3), 1141-1159.
  More info

  Abstract: We study the morphological content of a large sample of high-redshift clusters to determine its dependence on cluster mass and redshift. Quantitative morphologies are based on PSF-convolved, 2D bulge+disk decompositions of cluster and field galaxies on deep Very Large Telescope FORS2 images of eighteen, optically-selected galaxy clusters at 0.45 < z < 0.80 observed as part of the ESO Distant Cluster Survey ("EDisCS"). Morphological content is characterized by the early-type galaxy fraction fet, and early-type galaxies are objectively selected based on their bulge fraction and image smoothness. This quantitative selection is equivalent to selecting galaxies visually classified as E or S0. Changes in early-type fractions as a function of cluster velocity dispersion, redshift and star-formation activity are studied. A set of 158 clusters extracted from the Sloan Digital Sky Survey is analyzed exactly as the distant EDisCS sample to provide a robust local comparison. We also compare our results to a set of clusters from the Millennium Simulation. Our main results are: (1) the early-type fractions of the SDSS and EDisCS clusters exhibit no clear trend as a function of cluster velocity dispersion. (2) Mid-z EDisCS clusters around σ = 500 km s-1 have f et ∼ 0.5 whereas high-z EDisCS clusters have fet ∼ 0.4. This represents a ̃25% increase over a time interval of 2 Gyr. (3) There is a marked difference in the morphological content of EDisCS and SDSS clusters. None of the EDisCS clusters have early-type galaxy fractions greater than 0.6 whereas half of the SDSS clusters lie above this value. This difference is seen in clusters of all velocity dispersions. (4) There is a strong and clear correlation between morphology and star formation activity in SDSS and EDisCS clusters in the sense that decreasing fractions of [OII] emitters are tracked by increasing early-type fractions. This correlation holds independent of cluster velocity dispersion and redshift even though the fraction of [OII] emitters decreases from z ̃ to z ̃ in all environments. Our results pose an interesting challenge to structural transformation and star formation quenching processes that strongly depend on the global cluster environment (e.g., a dense ICM) and suggest that cluster membership may be of lesser importance than other variables in determining galaxy properties. © 2009 ESO.
• Sivanandam, S., Zabludoff, A. I., Zaritsky, D., Gonzalez, A. H., & Kelson, D. D. (2009). THE ENRICHMENT OF THE INTRACLUSTER MEDIUM. ASTROPHYSICAL JOURNAL, 691(2), 1787-1806.
• Sánchez-Blázquez, P., Jablonka, P., Noll, S., Poggianti, B. M., Moustakas, J., Milvang-Jensen, B., Halliday, C., Aragón-Salamanca, A., Saglia, R. P., Desai, V., Lucia, G. D., Clowe, D. I., Pelló, R., Rudnick, G., Simard, L., White, S. D., & Zaritsky, D. (2009). Evolution of red-sequence cluster galaxies from redshift 0.8 to 0.4: ages, metallicities, and morphologies. Astronomy and Astrophysics, 499(1), 47-68.
  More info

  Abstract: We present a comprehensive analysis of the stellar population properties and morphologies of red-sequence galaxies in 24 clusters and groups from to. The dataset, consisting of 215 spectra drawn from the ESO Distant Cluster Survey, constitutes the largest spectroscopic sample at these redshifts for which such an analysis has been conducted. Analysis reveals that the evolution of the stellar population properties of red-sequence galaxies depend on their mass: while the properties of the most massive are well described by passive evolution and high-redshift formation, those of the less massive galaxies are consistent with a more extended star-formation history. We show that these scenarios reproduce the index-σ relations and the galaxy colours. The two main results of this work are: (1) the evolution of the line-strength indices for the red-sequence galaxies can be reproduced if 40% of the galaxies with σ kms-1 entered the red-sequence between z = 0.75 to z = 0.45, in agreement with the fraction derived in studies of the luminosity functions; and (2) the percentage of red-sequence galaxies exhibiting early-type morphologies (E and S0) decreases by 20% from z = 0.75 to z = 0.45.. This can be understood if the red-sequence becomes more populated at later times with disc galaxies whose star formation has been quenched. We conclude that the processes quenching star formation do not necessarily produce a simultaneous morphological transformation of the galaxies entering the red-sequence. © 2009 ESO.
• Tran, K. H., Saintonge, A., Moustakas, J., Bai, L., Gonzalez, A. H., Holden, B. P., Zaritsky, D., & Kautsch, S. J. (2009). A SPECTROSCOPICALLY CONFIRMED EXCESS OF 24 mu m SOURCES IN A SUPER GALAXY GROUP AT z=0.37: ENHANCED DUSTY STAR FORMATION RELATIVE TO THE CLUSTER AND FIELD ENVIRONMENT. ASTROPHYSICAL JOURNAL, 705(1), 809-820.
• Tran, K. H., Saintonge, A., Moustakas, J., Bai, L., Gonzalez, A. H., Holden, B. P., Zaritsky, D., & Kautsch, S. J. (2009). A spectroscopically confirmed excess of 24 μm sources in a super galaxy group at z = 0.37: Enhanced dusty star formation relative to the cluster and field environment. Astrophysical Journal Letters, 705(1), 809-820.
  More info

  Abstract: To trace how dust-obscured star formation varies with environment, we compare the fraction of 24 μm sources in a super galaxy group to the field and a rich galaxy cluster at z ∼ 0.35. We draw on multi-wavelength observations9Based on observations made with (1) The ESO telescopes at Paranal Observatories under program IDs 072.A-0367, 076.B-0362, 078.B-0409; (2) the NASA/ESA Hubble Space Telescope (GO-10499); STScI is operated by the association of Universities for Research in Astronomy, Inc. under the NASA contract NAS 5-26555; (3) the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA; support for this work was provided by NASA through an award issued by JPL/Caltech (GO-20683); (4) the Chandra X-ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration under contract NAS8-03060; and (5) the Magellan 6.5 m telescope operated by OCIW. that combine Hubble, Chandra, and Spitzer imaging with extensive optical spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus ensure a uniform analysis. We focus on the four galaxy groups (σ1D = 303-580 km s -1) in supergroup 1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We find that (1) the fraction of supergroup galaxies with SFRIR ≥ 3 M ⊙ yr-1 is 4 times higher than in the cluster (32% ± 5% versus 7% 2%); (2) the supergroup's infrared luminosity function confirms that it has a higher density of IR members compared to the cluster and includes bright IR sources (log(L IR)[erg s-1] >45) not found in galaxy clusters at z ≲ 0.35; and (3) there is a strong trend of decreasing 24 μm fraction with increasing galaxy density, i.e., an infrared-density relation, not observed in the cluster. These dramatic differences are surprising because the early-type fraction in the supergroup is already as high as in clusters, i.e., the timescales for morphological transformation cannot be strongly coupled to when the star formation is completely quenched. The supergroup has a significant fraction (17%) of luminous, low-mass (10.0 < log(M *)[M ⊙] < 10.6), SFRIR ≥ 3 M ⊙ yr-1 members that are outside the group cores (R proj ≥ 0.5Mpc); once their star formation is quenched, most will evolve into faint red galaxies. Our analysis indicates that the supergroup's 24 μm population also differs from that in the field: (1) despite the supergroup having twice the fraction of E/S0s as the field, the fraction of SFRIR ≥ 3 M ⊙ yr-1 galaxies is comparable in both environments, and (2) the supergroup's IR luminosity function has a higher L*IR than that previously measured for the field. © 2009. The American Astronomical Society. All rights reserved.
• Varela, J., Zaritsky, D., White, S. D., Whiley, I. M., Varela, J. A., Simard, L., Sanchez-blazquez, P., Saglia, R. P., Rudnick, G., Poirier, S., Poggianti, B. M., Pello, R., Nowak, N., Noll, S., Moustakas, J., Milvang-jensen, B., Lucia, G. D., Linden, A. V., Johnson, O., , Jablonka, P., et al. (2009). The ESO distant cluster sample: galaxy evolution and environment out to z = 1. The Messenger, 136(136), 54-59.
  More info

  Steward Observatory, Tucson, USA The ESO Distant Cluster Survey (EDisCS, P.I. Simon D.M. White, LP 166.A-0162) is an ESO large programme aimed at studying clusters and cluster galaxies at z=0.4-1. How different is the evolution of the star formation activity in clusters, in groups and in the field? Does it depend on cluster mass and/or the local galaxy density? How relevant are starburst and post-starburst galaxies in the different environments? Is there an evolution in the galaxies' structures, and if so, is this related to the changes in their star formation activity? These are some of the main questions that have been investigated using the EDisCS dataset. There is no shortage of evidence that galaxy properties vary systematically with the environment in which they reside. The distributions of star formation histories, morphologies and masses, all strongly depend on galaxy location, at all redshifts probed so far. For large statistical studies, there are two main complementary ways to “measure” environment: the local galaxy number density (the number of galaxies per unit volume or projected area around the galaxy of interest), and the virial mass of the cluster or group where the galaxy resides, when this applies, usually derived from the velocity dispersion of the system. Traditionally, studies of the dependence of galaxy evolution on environment were largely based on cluster studies, and their comparison with the “field”. Recently, understanding the role of environment has become a major theme of all deep galaxy redshift surveys. Fully characterizing environment is a challenging task even for the largest field surveys, but great advances have been made in studying the local galaxy density as well as significant samples of groups at high-z. Even the widest area field surveys, however, include only a few distant massive systems. Only pointed surveys are able to probe galaxy clusters and massive groups, and to reach the high end of the local density distribution. Studies of galaxy clusters have traditionally opened the way to some of the major discoveries of galaxy evolution: to name a few, it is in clusters that astronomers first recognized the strong decline of the star formation activity in the last 7Gyr, the existence of a relation between local density and distribution of morphological types, the the fact that both star formation activity and mass assembly of massive ellipticals are completed at high-z, and the observed evolution of galaxy morphologies. Today, it has become possible to study galaxy evolution across a wide range of environments (clusters, groups, but also poor groups and the field), using optically selected cluster fields. Here we present one of such cluster surveys. The survey The ESO Distant Cluster Survey (hereafter, EDisCS) is a multiwavelength survey of galaxies in 20 fields containing galaxy clusters at z=0.4-1 based on an ESO Large Programme approved in P66.
• WHITE, S., & ZARITSKY, D. (2009). MODELS FOR GALAXY HALOS IN AN OPEN UNIVERSE. ASTROPHYSICAL JOURNAL, 394(1), 1-6.
• Whiley, I. M., Aragon-Salamanca, A., De Lucia, G., von der Linden, A., Bamford, S. P., Best, P., Bremer, M. N., Jablonka, P., Johnson, O., Milvang-Jensen, B., Noll, S., Poggianti, B. M., Rudnick, G., Saglia, R., White, S., & Zaritsky, D. (2009). The evolution of the brightest cluster galaxies since z similar to 1 from the ESO Distant Cluster Survey (EDisCS). MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 387(3), 1253-1263.
• Yang, Y., Zabludoff, A. I., Zaritsky, D., & Mihos, J. C. (2009). THE DETAILED EVOLUTION OF E+A GALAXIES INTO EARLY TYPES (vol 688, pg 945, 2008). ASTROPHYSICAL JOURNAL, 702(2), 1683-1683.
• Zaritsky, D., White, S. D., Simard, L., Saglia, R. P., Rudnick, G., Poggianti, B. M., Pello, R., Milvang-jensen, B., Marchesini, D., Lucia, G. D., Linden, A. V., Jablonka, P., Halliday, C., Clowe, D., & Aragon-salamanca, A. (2009). THE REST-FRAME OPTICAL LUMINOSITY FUNCTION OF CLUSTER GALAXIES AT z < 0.8 AND THE ASSEMBLY OF THE CLUSTER RED SEQUENCE*. The Astrophysical Journal, 700(2), 1559-1588. doi:10.1088/0004-637x/700/2/1559
  More info

  We present the rest-frame optical luminosity function (LF) of red-sequence galaxies in 16 clusters at 0.4 < z < 0.8 drawn from the ESO Distant Cluster Survey (EDisCS). We compare our clusters to an analogous sample from the Sloan Digital Sky Survey (SDSS) and match the EDisCS clusters to their most likely descendants. We measure all LFs down to M similar to M* + (2.5 -3.5). At z < 0.8, the bright end of the LF is consistent with passive evolution but there is a significant buildup of the faint end of the red sequence toward lower redshift. There is a weak dependence of the LF on cluster velocity dispersion for EDisCS but no such dependence for the SDSS clusters. We find tentative evidence that red-sequence galaxies brighter than a threshold magnitude are already in place, and that this threshold evolves to fainter magnitudes toward lower redshifts. We compare the EDisCS LFs with the LF of coeval red-sequence galaxies in the field and find that the bright end of the LFs agree. However, relative to the number of bright red galaxies, the field has more faint red galaxies than clusters at 0.6 < z < 0.8 but fewer at 0.4 < z < 0.6, implying differential evolution. We compare the total light in the EDisCS cluster red sequences to the total red-sequence light in our SDSS cluster sample. Clusters at 0.4 < z < 0.8 must increase their luminosity on the red sequence (and therefore stellar mass in red galaxies) by a factor of 1 -3 by z = 0. The necessary processes that add mass to the red sequence in clusters predict local clusters that are overluminous as compared to those observed in the SDSS. The predicted cluster luminosities can be reconciled with observed local cluster luminosities by combining multiple previously known effects.
• Bailin, J., Power, C., Norberg, P., Zaritsky, D., & Gibson, B. K. (2008). The anisotropic distribution of satellite galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 390(3), 1133-1156.
• Bailin, J., Power, C., Norberg, P., Zaritsky, D., & Gibson, B. K. (2008). The anisotropic distribution of satellite galaxies. Monthly Notices of the Royal Astronomical Society, 390(3), 1133-1156.
  More info

  Abstract: We identify satellites of isolated galaxies in the Sloan Digital Sky Survey and examine their angular distribution. Using mock catalogues generated from cosmological N-body simulations, we demonstrate that the selection criteria used to select isolated galaxies and their satellites in large galaxy redshift surveys must be very strict in order to correctly identify systems in which the primary galaxy dominates its environment. We demonstrate that the criteria used in many previous studies instead select predominantly group members. We refine a set of selection criteria for which the group contamination is estimated to be less than 7 per cent and present a catalogue of the resulting sample. The angular distribution of satellites about their host is biased towards the major axes for spheroidal galaxies and probably also for red disc galaxies (the 'intermediate' class of Bailin & Harris), but is isotropic for blue disc galaxies, i.e. it is the colour of the host that determines the distribution of its satellites rather than its morphology. The similar anisotropy measured in this study to studies that were dominated by groups implies that group-specific processes are not responsible for the angular distribution. Satellites that are most likely to have been recently accreted, late-type galaxies at large projected radii, show a tendency to lie along the same axis as the surrounding large-scale structure. The orientations of isolated early- and intermediate-type galaxies also align with the surrounding large-scale structures. We discuss the origin of the anisotropic satellite distribution and consider the implications of our results, critically assessing the respective roles played by the orientation of the visible galaxy within its dark matter halo, anisotropic accretion of satellites from the larger scale environment, and the biased nature of satellites as tracers of the underlying dark matter subhalo population. © 2008 The Authors.
• Bernard, J., Reach, W. T., Paradis, D., Meixner, M., Paladini, R., Kawamura, A., Onishi, T., Vijh, U., Gordon, K., Indebetouw, R., Hora, J. L., Whitney, B., Blum, R., Meade, M., Babler, B., Churchwell, E. B., Engelbracht, C. W., For, B., Misselt, K., , Leitherer, C., et al. (2008). Spitzer survey of the large magellanic cloud, surveying the agents of a galaxy's evolution (sage). IV. dust properties in the interstellar medium. Astronomical Journal, 136(3), 919-945.
  More info

  Abstract: The goal of this paper is to present the results of a preliminary analysis of the extended infrared (IR) emission by dust in the interstellar medium (ISM) of the Large Magellanic Cloud (LMC). We combine Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and Infrared Astronomical Satellite (IRAS) data and correlate the infrared emission with gas tracers of H I, CO, and H α. We present a global analysis of the infrared emission as well as detailed modeling of the spectral energy distribution (SED) of a few selected regions. Extended emission by dust associated with the neutral, molecular, and diffuse ionized phases of the ISM is detected at all IR bands from 3.6 μm to 160 μm. The relative abundance of the various dust species appears quite similar to that in the Milky Way (MW) in all the regions we have modeled. We construct maps of the temperature of large dust grains. The temperature map shows variations in the range 12.1-34.7 K, with a systematic gradient from the inner to outer regions, tracing the general distribution of massive stars and individual H II regions as well as showing warmer dust in the stellar bar. This map is used to derive the far-infrared (FIR) optical depth of large dust grains. We find two main departures in the LMC with respect to expectations based on the MW: (1) excess mid-infrared (MIR) emission near 70 μm, referred to as the 70 μm excess, and (2) departures from linear correlation between the FIR optical depth and the gas column density, which we refer to as FIR excess emission. The 70 μm excess increases gradually from the MW to the LMC to the Small Magellanic Cloud (SMC), suggesting evolution with decreasing metallicity. The excess is associated with the neutral and diffuse ionized gas, with the strongest excess region located in a loop structure next to 30 Dor. We show that the 70 μm excess can be explained by a modification of the size distribution of very small grains with respect to that in the MW, and a corresponding mass increase of ≃13% of the total dust mass in selected regions. The most likely explanation is that the 70 μm excess is due to the production of large very small grains (VSG) through erosion of larger grains in the diffuse medium. This FIR excess could be due to intrinsic variations of the dust/gas ratio, which would then vary from 4.6 to 2.3 times lower than the MW values across the LMC, but X CO values derived from the IR emission would then be about three times lower than those derived from the Virial analysis of the CO data. We also investigate the possibility that the FIR excess is associated with an additional gas component undetected in the available gas tracers. Assuming a constant dust abundance in all ISM phases, the additional gas component would have twice the known H I mass. We show that it is plausible that the FIR excess is due to cold atomic gas that is optically thick in the 21 cm line, while the contribution by a pure H2 phase with no CO emission remains a possible explanation. © 2008. The American Astronomical Society. All rights reserved.
• Christlein, D., & Zaritsky, D. (2008). Kinematic properties of the extended disks of spiral galaxies: A sample of edge-on galaxies. ASTROPHYSICAL JOURNAL, 680(2), 1053-1071.
• Christlein, D., & Zaritsky, D. (2008). The kinematic properties of the extended disks of spiral galaxies: A sample of edge-on galaxies. Astrophysical Journal, 680(2), 1053-1071.
  More info

  Abstract: We present a kinematic study of the outer regions (R25 < R < 2R25) of 17 edge-on disk galaxies. Using deep long-slit spectroscopy (flux sensitivity ∼few 10-19 erg s-1 cm-2 arcsec-2), we search for Hα emission, which must be emitted at these flux levels by any accumulation of hydrogen due to the presence of the extragalactic UV background and any other local source of UV flux. We present results from the individual galaxy spectra and a stacked composite. We detect Ha in many cases well beyond R25 and sometimes as far as 2R25. The combination of sensitivity, spatial resolution, and kinematic resolution of this technique thus provides a powerful complement to 21 cm observations. Kinematics in the outer disk are generally disklike (flat rotation curves, small velocity dispersions) at all radii, and there is no evidence for a change in the velocity dispersion with radius. We place strong limits, a few percent, on the existence of counterrotating gas out to 1.5R 25. These results suggest that thin disks extend well beyond R 25; however, we also find a few puzzling anomalies. In ESO 323-G033 we find two emission regions that have velocities close to the systemic velocity rather than the expected rotation velocity. These low relative velocities are unlikely to be simply due to projection effects and so suggest that these regions are not on disk-plane, circular orbits. In MCG -01-31 -002 we find emission from gas with a large velocity dispersion that is corotating with the inner disk. © 2008. The American Astronomical Society. All rights reserved.
• Dalcanton, J. J., Williams, B. F., Seth, A. C., Dolphin, A., Holtzman, J., Rosema, K., Skillman, E. D., Cole, A., Girardi, L., Gogarten, S. M., Karachentsev, I. D., Olsen, K., Weisz, D., Christensen, C., Freeman, K., Gilbert, K., Gallart, C., Harris, J., Hodge, P., , de Jong, R. S., et al. (2008). THE ACS NEARBY GALAXY SURVEY TREASURY. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 183(1), 67-108.
• De Lucia, G., Weinmann, S., Poggianti, B. M., Aragon-Salamanca, A., & Zaritsky, D. (2008). The environmental history of group and cluster galaxies in a Lambda cold dark matter universe. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 423(2), 1277-1292.
• De, J., Harris, J., Coleman, M. G., Martin, N. F., Bell, E. F., Rix, H. -., Hill, J. M., Skillman, E. D., Sand, D. J., Olszewski, E. W., Zaritsky, D., Thompson, D., Giallongo, E., Ragazzoni, R., DiPaola, A., Farinato, J., Testa, V., & Bechtold, J. (2008). The structural properties and star formation history of Leo T from deep LBT photometry. ASTROPHYSICAL JOURNAL, 680(2), 1112-1119.
• Finn, R. A., Balogh, M. L., Zaritsky, D., Miller, C. J., & Nichol, R. C. (2008). Mass and redshift dependence of star formation in relaxed galaxy clusters. ASTROPHYSICAL JOURNAL, 679(1), 279-292.
• Finn, R. A., Balogh, M. L., Zaritsky, D., Miller, C. J., & Nichol, R. C. (2008). Mass and redshift dependence of star formation in relaxed galaxy clusters. Astrophysical Journal, 679(1), 279-292.
  More info

  Abstract: We investigate the star formation properties of dynamically relaxed galaxy clusters as a function of cluster mass for 308 low-redshift clusters drawn from the Sloan Digital Sky Survey (SDSS) C4 cluster catalog. It is important to establish if cluster star formation properties have a mass dependence before comparing clusters at different epochs, and here we use cluster velocity dispersion, σ, as a measure of cluster mass. We select clusters with no significant substructure, a subset of the full C4 sample, so that velocity dispersion is an accurate tracer of cluster mass. We find that the total stellar mass, the number of star-forming galaxies, and total star formation rate scale linearly with the number of member galaxies, with no residual dependence on cluster velocity dispersion. With the mass-dependence of cluster star formation rates established, we compare the SDSS clusters with a sample of z ≃ 0.75 clusters from the literature and find that on average (correcting for the mass growth of clusters between the two redshifts) the total Ha luminosity of the high-redshift clusters is 10 times greater than that of the low-redshift clusters. This can be explained by a decline in the Ha luminosities of individual cluster galaxies by a factor of up to ∼10 since z ≃ 0.75. The magnitude of this evolution is comparable to that of field galaxies over a similar redshift interval, and thus the effect of the cluster environment on the evolution of star-forming galaxies is at most modest. Our results suggest that the physical mechanism driving the evolution of cluster star formation rates is independent of cluster mass, at least for clusters with velocity dispersion greater than 450 km s_1, and operates over a fairly long timescale such that the star formation rates of individual galaxies decline by an order of magnitude over ∼7 billion years. © 2008. The American Astronomical Society. All rights reserved.
• Gonzalez, A., Zabludoff, A., Zaritsky, D., & Dalcanton, J. (2008). Measuring the diffuse optical light in Abell 1651. ASTROPHYSICAL JOURNAL, 536(2), 561-570.
• Gordon, K. D., Meixner, M., Blum, R. D., Reach, W., Whitney, B. A., Harris, J., Indebetouw, R., Bolatto, A. D., Bernard, J. -., Sewilo, M., Babler, B. L., Block, M., Bot, C., Bracker, S., Carlson, L., Churchwell, E., Clayton, G. C., Cohen, M., Engelbracht, C. W., , Fukui, Y., et al. (2008). Early results from the SAGE-SMC Spitzer legacy. Proceedings of the International Astronomical Union, 4(S256), 184-188.
  More info

  Abstract: Early results from the SAGE-SMC (Surveying the Agents of Galaxy Evolution in the tidally-disrupted, low-metallicity Small Magellanic Cloud) Spitzer legacy program are presented. These early results concentrate on the SAGE-SMC MIPS observations of the SMC Tail region. This region is the high H i column density portion of the Magellanic Bridge adjacent to the SMC Wing. We detect infrared dust emission and measure the gas-to-dust ratio in the SMC Tail and find it similar to that of the SMC Body. In addition, we find two embedded cluster regions that are resolved into multiple sources at all MIPS wavelengths. © 2009 International Astronomical Union.
• Harris, J., & Zaritsky, D. (2008). THE STAR FORMATION HISTORY OF THE LARGE MAGELLANIC CLOUD. ASTRONOMICAL JOURNAL, 138(5), 1243-1260.
• Harris, J., & Zaritsky, D. (2008). The formation of Constellation III in the Large Magellanic Cloud. PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF AUSTRALIA, 25(3), 116-120.
• Harris, J., & Zaritsky, D. (2008). The formation of Constellation III in the Large Magellanic Cloud. Publications of the Astronomical Society of Australia, 25(3), 116-120.
  More info

  Abstract: We present a detailed reconstruction of the star-formation history of the Constellation III region in the Large Magellanic Cloud, to constrain the formation mechanism of this enigmatic feature. Star formation in Constellation III seems to have taken place during two distinct epochs: there is the 8-15 Myr epoch that had previously been recognized, but we also see strong evidence for a separate 'burst' of star formation 25-30 Myr ago. The 'super-supernova' or GRB blast wave model for the formation of Constellation III is difficult to reconcile with such an extended, two-epoch star formation history, because the shock wave should have induced star formation throughout the structure simultaneously, and any unconsumed gas would quickly be dissipated, leaving nothing from which to form a subsequent burst of activity. We propose a 'truly stochastic' self-propagating star formation model, distinct from the canonical model in which star formation proceeds in a radially directed wave from the center of Constellation III to its perimeter. As others have noted, and we now confirm, the bulk age gradients demanded by such a model are simply not present in Constellation III. In our scenario, the prestellar gas is somehow pushed into these large-scale arc structures, without simultaneously triggering immediate and violent star formation throughout the structure. Rather, star formation proceeds in the arc according to the local physical conditions of the gas. Self-propagating star formation is certainly possible, but in a truly stochastic manner, without a directed, large scale pattern. © Astronomical Society of Australia 2008.
• Herbert-Fort, S., Zaritsky, D., Kim, Y. J., Bailin, J., & Taylor, J. E. (2008). The orbital distribution of satellite galaxies. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 384(2), 803-813.
• Herbert-Fort, S., Zaritsky, D., Kim, Y. J., Bailin, J., & Taylor, J. E. (2008). The orbital distribution of satellite galaxies. Monthly Notices of the Royal Astronomical Society, 384(2), 803-813.
  More info

  Abstract: We measure the distribution of velocities for prograde and retrograde satellite galaxies using a combination of published data and new observations for 78 satellites of 63 extremely isolated disc galaxies (169 satellites total). We find that the velocity distribution is non-Gaussian (>99.9 per cent confidence), but that it can be described as the sum of two Gaussians, one of which is broad (σ = 176 ± 15 km s-1), has a mean prograde velocity of 86 ± 30 km s-1, and contains ∼55 per cent of the satellites, while the other is slightly retrograde with a mean velocity of -21 ± 22 km s-1 and σ = 74 ± 18 km s-1 and contains ∼45 per cent of the satellites. Both of these components are present over all projected radii and found in the sample regardless of cuts on primary inclination or satellite disc angle. The double-Gaussian shape, however, becomes more pronounced among satellites of more luminous primaries. We remove the potential dependence of satellite velocity on primary luminosity using the Tully-Fisher relation and still find the velocity distribution to be asymmetric and even more significantly non-Gaussian. The asymmetric velocity distribution demonstrates a connection between the inner, visible disc galaxy, and the kinematics of the outer, dark halo. The reach of this connection, extending even beyond the virial radii, suggests that it is imprinted by the satellite infall pattern and large-scale effects, rather than by higher level dynamical processes in the formation of the central galaxy or late-term evolution of the satellites. © 2008 RAS.
• Kautsch, S. J., Gonzalez, A. H., Soto, C. A., Tran, K. H., Zaritsky, D., & Moustakas, J. (2008). FORMING EARLY-TYPE GALAXIES IN GROUPS PRIOR TO CLUSTER ASSEMBLY. ASTROPHYSICAL JOURNAL LETTERS, 688(1), L5-L8.
• Kautsch, S. J., Gonzalez, A. H., Soto, C. A., Tran, K. H., Zaritsky, D., & Moustakas, J. (2008). Forming early-type galaxies in groups prior to cluster assembly. Astrophysical Journal, 687(1 PART 2), L5-L8.
  More info

  Abstract: We study a unique protocluster of galaxies, the supergroup SG1120-1202. We quantify the degree to which morphological transformation of cluster galaxies occurs prior to cluster assembly in order to explain the observed early-type fractions in galaxy clusters at z=0. SG1120-1202 at z ∼ 0.37 is composed of four gravitationally bound groups that are expected to coalesce into a single cluster by z=0. Using HST ACS observations, we compare the morphological fractions of the supergroup galaxies to those found in a range of environments. We find that the morphological fractions of early-type galaxies (-60%) and the ratio of SO to elliptical galaxies (0.5) in SG1120-1202 are very similar to clusters at comparable redshift, consistent with preprocessing in the group environment playing the dominant role in establishing the observed early-type fraction in galaxy clusters. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Kautsch, S. J., Gonzalez, A. H., Soto, C. A., Tran, K. H., Zaritsky, D., & Moustakas, J. (2008). Forming early-type galaxies in groups prior to cluster assembly. Astrophysical Journal, 688(1 PART 2), L5-L8.
  More info

  Abstract: We study a unique protocluster of galaxies, the supergroup SG1120-1202. We quantify the degree to which morphological transformation of cluster galaxies occurs prior to cluster assembly in order to explain the observed early-type fractions in galaxy clusters at z p 0. SG1120-1202 at z-0.37 is composed of four gravitationally bound groups that are expected to coalesce into a single cluster by z p 0. Using HST ACS observations, we compare the morphological fractions of the supergroup galaxies to those found in a range of environments. We find that the morphological fractions of early-type galaxies (∼60%) and the ratio of S0 to elliptical galaxies (0.5) in SG1120-1202 are very similar to clusters at comparable redshift, consistent with preprocessing in the group environment playing the dominant role in establishing the observed early-type fraction in galaxy clusters. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Milvang-Jensen, B., Noll, S., Halliday, C., Poggianti, B. M., Jablonka, P., Aragon-Salamanca, A., Saglia, R. P., Nowak, N., von, d., De, L. G., Pello, R., Moustakas, J., Poirier, S., Bamford, S. P., Clowe, D. I., Dalcanton, J. J., Rudnick, G. H., Simard, L., White, S., & Zaritsky, D. (2008). Spectroscopy of clusters in the ESO distant cluster survey (EDisCS). II. Redshifts, velocity dispersions, and substructure for clusters in the last 15 fields. ASTRONOMY & ASTROPHYSICS, 482(2), 419-449.
• Milvang-Jensen, B., Noll, S., Halliday, C., Poggianti, B. M., Jablonka, P., Aragón-Salamanca, A., Saglia, R. P., Nowak, N., Von, A., Lucia, G. D., Pelló, R., Moustakas, J., Poirier, S., Bamford, S. P., Clowe, D. I., Dalcanton, J. J., Rudnick, G. H., Simard, L., White, S. D., & Zaritsky, D. (2008). Spectroscopy of clusters in the ESO distant cluster survey (EDisCS). II.. Astronomy and Astrophysics, 482(2), 419-449.
  More info

  Abstract: Aims. We present spectroscopic observations of galaxies in 15 survey fields as part of the ESO Distant Cluster Survey (EDisCS). We determine the redshifts and velocity dispersions of the galaxy clusters located in these fields, and we test for possible substructure in the clusters.Methods. We obtained multi-object mask spectroscopy using the FORS2 instrument at the VLT. We reduced the data with particular attention to the sky subtraction. We implemented the method of Kelson for performing sky subtraction prior to any rebinning/interpolation of the data. From the measured galaxy redshifts, we determine cluster velocity dispersions using the biweight estimator and test for possible substructure in the clusters using the Dressler-Shectman test.Results. The method of subtracting the sky prior to any rebinning/interpolation of the data delivers photon-noise-limited results, whereas the traditional method of subtracting the sky after the data have been rebinned/interpolated results in substantially larger noise for spectra from tilted slits. Redshifts for individual galaxies are presented and redshifts and velocity dispersions are presented for 21 galaxy clusters. For the 9 clusters with at least 20 spectroscopically confirmed members, we present the statistical significance of the presence of substructure obtained from the Dressler-Shectman test, and substructure is detected in two of the clusters.Conclusions. Together with data from our previous paper, spectroscopy and spectroscopic velocity dispersions are now available for 26 EDisCS clusters with redshifts in the range 0.40-0.96 and velocity dispersions in the range . © 2008 ESO.
• Poggianti, B. M., Desai, V., Finn, R., Bamford, S., Lucia, G. D., Varela, J., Aragón-Salamanca, A., Halliday, C., Noll, S., Saglia, R., Zaritsky, D., Best, P., Clowe, D., Milvang-Jensen, B., Jablonka, P., Pelló, R., Rudnick, G., Simard, L., Von, A., & White, S. (2008). The relation between star formation, morphology, and local density in high-redshift clusters and groups. Astrophysical Journal, 684(2), 888-904.
  More info

  Abstract: We investigate how the [O II] properties and the morphologies of galaxies in clusters and groups at z = 0.4-0.8 depend on projected local galaxy density, and compare with the field at similar redshifts and clusters at low z. In both nearby and distant clusters, higher density regions contain proportionally fewer star-forming galaxies, and the aver-age [O II] equivalent width of star-forming galaxies is independent of local density. However, in distant clusters the average current star formation rate (SFR) in star-forming galaxies seems to peak at densities ∼15-40 galaxies Mpc-2. At odds with low-z results, at high z the relation between star-forming fraction and local density varies from high- to low-mass clusters. Overall, our results suggest that at high z the current star formation (SF) activity in star-forming galaxies does not depend strongly on global or local environment, though the possible SFR peak seems at odds with this conclusion. We find that the cluster SFR normalized by cluster mass anticorrelates with mass and correlates with the star-forming fraction. These trends can be understood given (1) that the average star-forming galaxy forms about 1 M⊙ yr-1 (uncorrected for dust) in all clusters; (2) that the total number of galaxies scales with cluster mass; and (3) the dependence of star-forming fraction on cluster mass. We present the morphology-density (MD) relation for our z = 0.4 - 0.8 clusters, and uncover that the decline of the spiral fraction with density is entirely driven by galaxies of type Sc or later. For galaxies of a given Hubble type, we see no evidence that SF properties depend on local environment. In contrast with recent findings at low z, in our distant clusters the SF-density relation and the MD relation are equivalent, suggesting that neither of the two is more fundamental than the other. © 2008. The American Astronomical Society. All rights reserved.
• Sand, D. J., Zaritsky, D., Herbert-Fort, S., Sivanandam, S., & Clowe, D. (2008). A photometric search for transients in galaxy clusters. ASTRONOMICAL JOURNAL, 135(5), 1917-1933.
• Sand, D. J., Zaritsky, D., Herbert-Fort, S., Sivanandam, S., & Clowe, D. (2008). A photometric search for transients in galaxy clusters. Astronomical Journal, 135(5), 1917-1933.
  More info

  Abstract: We have begun a program to search for supernovae and other transients in the fields of galaxy clusters with the 2.3 m Bok Telescope on Kitt Peak. We present our automated photometric methods for data reduction, efficiency characterization, and initial spectroscopy. With this program, we aim to ultimately identify 25-35 cluster Type Ia supernovae (SNe Ia) (10 of which will be intracluster, hostless events) and constrain the SN Ia rate associated with old, passive stellar populations. With these measurements we will constrain the relative contribution of hostless and hosted SNe Ia to the metal enrichment of the intracluster medium. In the current work, we have identified a central excess of transient events within 1.25r 200 in our cluster fields after statistically subtracting out the "background" transient rate taken from an off-cluster CCD chip. Based on the published rate of SNe Ia for cluster populations we estimate that 20% of the excess cluster transients are due to cluster SNe Ia, a comparable fraction to core collapse (CC) supernovae and the remaining are likely to be active galactic nuclei. Interestingly, we have identified three intracluster SN candidates, all of which lay beyond R > r 200. These events, if truly associated with the cluster, indicate a large deficit of intracluster (IC) SNe at smaller radii, and may be associated with the IC stars of infalling groups or indicate that the intracluster light (ICL) in the cluster outskirts is actively forming stars which contribute CC SNe or prompt SNe Ia. © 2008. The American Astronomical Society. All rights reserved.
• Tran, K. H., Moustakas, J., Gonzalez, A. H., Bai, L., Zaritsky, D., & Kautsch, S. J. (2008). The late stellar assembly of massive cluster galaxies via major merging. ASTROPHYSICAL JOURNAL LETTERS, 683(1), L17-L20.
• Tran, K. H., Moustakas, J., Gonzalez, A. H., Bai, L., Zaritsky, D., & Kautsch, S. J. (2008). The late stellar assembly of massive cluster galaxies via major merging. Astrophysical Journal, 683(1 PART 2), L17-L20.
  More info

  Abstract: We present multiwavelength observations of the brightest galaxies in four X-ray-luminous groups at z-0.37 that will merge to form a cluster comparable in mass to Coma. Ordered by increasing stellar mass, the four brightest group galaxies (BGGs) present a time sequence where BGG-1, 2, and 3 are in merging systems and BGG-4 is a massive remnant (M* p 6.7 x 10 11 M⊙). BGG-1 and 2 have bright, gravitationally bound companions and BGG-3 has two nuclei separated by only 2.5 kpc; thus, merging atz < 0.5 increases the BGG mass by ⊙40% (t MGR < 2 Gyr) and V-band luminosity by-0.4 mag. The BGGs' rest-frame (B-V) colors correspond to stellar ages of >3 Gyr, and their tight scatter in (B-V) color (σBV=0.032) confirms that they formed the bulk of their stars at z > 0.9. Optical spectroscopy shows no signs of recent (
• Tran, K. H., Moustakas, J., Gonzalez, A. H., Bai, L., Zaritsky, D., & Kautsch, S. J. (2008). The late stellar assembly of massive cluster galaxies via major merging. Astrophysical Journal, 684(1 PART 2), L17-L20.
  More info

  Abstract: We present multiwavelength observations of the brightest galaxies in four X-ray-luminous groups at z-0.37 that will merge to form a cluster comparable in mass to Coma. Ordered by increasing stellar mass, the four brightest group galaxies (BGGs) present a time sequence where BGG-1, 2, and 3 are in merging systems and BGG-4 is a massive remnant (M=6.7 x 1011 M&o.). BGG-1 and 2 have bright, gravitationally bound companions and BGG-3 has two nuclei separated by only 2.5 kpc; thus, merging atz < 0.5 increases the BGG mass by ⊙40% (t MGR < 2 Gyr) and V-band luminosity by-0.4 mag. The BGGs' rest-frame (B-V) colors correspond to stellar ages of >3 Gyr, and their tight scatter in (B-V) color (σBV p 0.032) confirms that they formed the bulk of their stars at z > 0.9. Optical spectroscopy shows no signs of recent (
• Walsh, S. M., Willman, B., Sand, D., Harris, J., Seth, A., Zaritsky, D., & Jerjen, H. (2008). Boötes II reboöted: An MMT/Megacam study of an ultrafaint Milky Way satellite. Astrophysical Journal, 688(1), 245-253.
  More info

  Abstract: We present MMT/Megacam imaging in Sloan g and r of the extremely low luminosity Bootes II Milky Way companion. We use a bootstrap approach to perform robust measurements of, and to calculate uncertainties on, Boötes II's distance, luminosity, size, and morphology. Comparisons with theoretical isochrones and empirical globular cluster fiducials show that Boötes II's stellar population is old and metal-poor ([Fe/H] ≲ -2). Assuming a stellar population like that of M92, Boötes II is at a distance of 42 ± 2 kpc, closer than the initial published estimate of 60 ± 10 kpc. This distance revision, combined with a more robust measurement of Boötes II's structure with both a Plummer model and an exponential model, results in more compact inferred physical half-light sizes of rh ≃ 36 ± 9 and 33 ± 10 pc, respectively, and lower-limit inferred luminosities of MV ≃ -2.4 ± 0.7 and -2.2 ± 0.7 mag, respectively. Our revised size and luminosity calculations move Boötes II into a region of size-luminosity space not previously known to be occupied by old stellar populations, but also occupied by the recently discovered Milky Way satellites Willman 1 and Segue 1. We show that the apparently distorted morphology of Boötes II is not statistically significant given the present data. We use a tidal argument to support a scenario in which Boötes II is a dwarf galaxy (dark matter-dominated) rather than a globular cluster (not dark matter-dominated), although our inferred uncertainty on the M/L for Boötes II is substantial. Moreover, we cannot rule out the possibility that Boötes II is a star cluster on the verge of disruption like Palomar 5. © 2008, The American Astronomical Society. All rights reserved.
• Whiley, I. M., Aragón-Salamanca, A., Lucia, G. D., Von, A., Bamford, S. P., Best, P., Bremer, M. N., Jablonka, P., Johnson, O., Milvang-Jensen, B., Noll, S., Poggianti, B. M., Rudnick, G., Saglia, R., White, S., & Zaritsky, D. (2008). The evolution of the brightest cluster galaxies since z ∼ 1 from the ESO Distant Cluster Survey (EDisCS). Monthly Notices of the Royal Astronomical Society, 387(3), 1253-1263.
  More info

  Abstract: We present K-band data for the brightest cluster galaxies (BCGs) from the ESO Distant Cluster Survey (EDisCS). These data are combined with the photometry published by Aragón-Salamanca, Baugh & Kauffmann and a low-redshift comparison sample built from the BCG catalogue of von der Linden et al. BCG luminosities are measured inside a metric circular aperture with 37 kpc diameter. In agreement with previous studies, we find that the K-band Hubble diagram for BCGs exhibits very low scatter (∼0.35) over a redshift range of 0 < z < 1. The colour and rest-frame K-band luminosity evolution of the BCGs are in good agreement with population synthesis models of stellar populations which formed at z > 2 and evolved passively thereafter. In contrast with some previous studies, we do not detect any significant change in the stellar mass of the BCG since z ∼ 1. These results do not seem to depend on the velocity dispersion of the parent cluster. We also find that there is a correlation between the 1D velocity dispersion of the clusters (σcl) and the K-band luminosity of the BCGs (after correcting for passive-evolution). The clusters with large velocity dispersions, and therefore masses, tend to have brighter BCGs, i.e. BCGs with larger stellar masses. This dependency, although significant, is relatively weak: the stellar mass of the BCGs changes only by ∼70 per cent over a two order of magnitude range in cluster mass. Furthermore, this dependency does not change significantly with redshift. We have compared our observational results with the hierarchical galaxy formation and evolution model predictions of De Lucia & Blaizot. We find that the models predict colours which are in reasonable agreement with the observations because the growth in stellar mass is dominated by the accretion of old stars. However, the stellar mass in the model BCGs grows by a factor of 3-4 since z = 1, a growth rate which seems to be ruled out by the observations. The models predict a dependency between the BCG's stellar mass and the velocity dispersion (mass) of the parent cluster in the same sense as the data, but the dependency is significantly stronger than observed. However, one major difficulty in this comparison is that we have measured magnitudes inside a fixed metric aperture while the models compute total luminosities. © 2008 The Authors.
• Whitney, B. A., Sewilo, M., Indebetouw, R., Robitaille, T. P., Meixner, M., Gordon, K., Meade, M. R., Babler, B. L., Harris, J., Hora, J. L., Bracker, S., Povich, M. S., Churchwell, E. B., Engelbracht, C. W., For, B. -., Block, M., Misselt, K., Vijh, U., Leitherer, C., , Kawamura, A., et al. (2008). Spitzer sage survey of the large magellanic cloud. III. Star formation and 1000 new candidate young stellar objects. Astronomical Journal, 136(1), 18-43.
  More info

  Abstract: We present 1000 new candidate Young Stellar Objects (YSOs) in the Large Magellanic Cloud selected from Spitzer Space Telescope data, as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) Legacy program. The YSOs, detected by their excess infrared (IR) emission, represent early stages of evolution, still surrounded by disks and/or infalling envelopes. Previously, fewer than 20 such YSOs were known. The candidate YSOs were selected from the SAGE Point Source Catalog from regions of color-magnitude space least confused with other IR-bright populations. The YSOs are biased toward intermediate- to high-mass and young evolutionary stages, because these overlap less with galaxies and evolved stars in color-magnitude space. The YSOs are highly correlated spatially with atomic and molecular gas, and are preferentially located in the shells and bubbles created by massive stars inside. They are more clustered than generic point sources, as expected if star formation occurs in filamentary clouds or shells. We applied a more stringent color-magnitude selection to produce a subset of "high-probability" YSO candidates. We fitted the spectral-energy distributions (SEDs) of this subset and derived physical properties for those that were well fitted. The total mass of these well-fitted YSOs is 2900 M and the total luminosity is 2.1 × 10 6 L . By extrapolating the mass function with a standard initial mass function and integrating, we calculate a current star-formation rate of 0.06 M yr-1, which is at the low end of estimates based on total ultraviolet and IR flux from the galaxy (0.05 - 0.25 M yr-1), consistent with the expectation that our current YSO list is incomplete. Follow-up spectroscopy and further data mining will better separate the different IR-bright populations and likely increase the estimated number of YSOs. The full YSO list is available as electronic tables, and the SEDs are available as an electronic figure for further use by the scientific community. © 2008. The American Astronomical Society. All rights reserved..
• Willman, B., Harris, J., Zaritsky, D., Sand, D. J., Zaritsky, D., Willman, B., Walsh, S. M., Seth, A. C., Sand, D. J., Jerjen, H., & Harris, J. (2008). BOÖTES II REBOÖTED : AN MMT/MEGACAM STUDY OF AN ULTRAFAINT MILKY WAY SATELLITE. The Astrophysical Journal, 688(1), 245-253. doi:10.1086/592076
  More info

  We present MMT/Megacam imaging in Sloan g and r of the extremely low luminosity Bo?tes II Milky Way companion. We use a bootstrap approach to perform robust measurements of, and to calculate uncertainties on, Bo?tes II's distance, luminosity, size, and morphology. Comparisons with theoretical isochrones and empirical globular cluster fiducials show that Bo?tes II's stellar population is old and metal-poor ( -->[Fe/H] ? 2). Assuming a stellar population like that of M92, Bo?tes II is at a distance of -->42 ? 2 kpc, closer than the initial published estimate of -->60 ? 10 kpc. This distance revision, combined with a more robust measurement of Bo?tes II's structure with both a Plummer model and an exponential model, results in more compact inferred physical half-light sizes of -->rh 36 ? 9 and -->33 ? 10 pc, respectively, and lower-limit inferred luminosities of -->MV ? 2.4 ? 0.7 and -->-2.2 ? 0.7 mag, respectively. Our revised size and luminosity calculations move Bo?tes II into a region of size-luminosity space not previously known to be occupied by old stellar populations, but also occupied by the recently discovered Milky Way satellites Willman 1 and Segue 1. We show that the apparently distorted morphology of Bo?tes II is not statistically significant given the present data. We use a tidal argument to support a scenario in which Bo?tes II is a dwarf galaxy (dark matter-dominated) rather than a globular cluster (not dark matter-dominated), although our inferred uncertainty on the -->M/L for Bo?tes II is substantial. Moreover, we cannot rule out the possibility that Bo?tes II is a star cluster on the verge of disruption like Palomar 5.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., Yang, Y., & Mihos, J. C. (2008). The Detailed Evolution of E+A Galaxies into Early Types. The Astrophysical Journal, 688(2), 945-971. doi:10.1086/591656
  More info

  Poststarburst, or E+A, galaxies are the best candidates for galaxies in transition from being gas-rich and star- forming to gas-poor and passively evolving as a result of galaxy-galaxy interactions. To focus on what E+A galaxies become after their young stellar populations fade away, we present the detailed morphologies of 21 E+A galaxies using high-resolution HSTACS and WFPC2 images. Most of these galaxies lie in the field, well outside of rich clus- ters, and at least 55 (15%) have dramatic tidal features indicative of mergers. Our sample includes one binary E+A system, in which both E+As are tidally disturbed and interacting with each other. Our E+As are similar to early types inthattheyhavelargebulgeYtoYtotallightratios(medianB/T ¼ 0:59),highSersicindices(nk4),andhighconcen- trationindices(Ck4:3),buttheyhaveconsiderablylargerasymmetry indices(Ak0:04)thanellipticals,presumably due to the disturbances within a fewre caused by the starburst and/or the galaxy-galaxy interaction. We conclude that E+Aswillbemorphologicallyclassifiedasearly-typegalaxiesoncethesedisturbancesandthelowsurfacebrightness tidal features fade. The color morphologies are diverse, including six E+As with compact (0.4Y1.4 kpc) blue cores, which might be local analogs of high-z ellipticals with blue cores. The large fraction (70%) of E+As with positive colorgradientsindicatesthattheyoungstellarpopulationsaremoreconcentratedthantheold.Thesepositivecolor gradients (i.e., bluer nuclei) could evolve into the negative gradients typical in E/S0s if the central parts of these galaxies are metal-enhanced. Our E+As stand apart from the E/S0s in the edge-on projection of the fundamental plane (FP), implying that their stellar populations differ from those of E/S0s and that E+As have, on average, a M/L that is 3.8 times smaller. The tilt of the E+A FP indicates that the variation among their stellar populations is closely tied to the structural parameters; i.e., E+As follow their own scaling relationships such that smaller or less massive galaxies have smaller M/L. Wefind a population of unresolved compact sources in nineE+As (45%), all of which havemerger signatures. In the four E+As with suitable color data, the compact sources have colors and luminosities consistent with newly formed star clusters. The bright end of the cluster LF is fainter in redder E+As, suggesting that the young star clusters fade or are disrupted as the merger remnant ages. In summary, the morphologies, color profiles, scaling relations, and cluster populations are all consistent with E+As evolving ultimately into early types, making the study of E+As critical to understanding the origin of the red sequence of galaxies. Subject headingg galaxies: evolution — galaxies: interactions — galaxies: starburst — galaxies: star clusters — galaxies: stellar content
• Zaritsky, D., & Rix, H. (2008). Lopsided spiral galaxies and a limit on the galaxy accretion rate. ASTROPHYSICAL JOURNAL, 477(1), 118-&.
• Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2008). Toward equations of galactic structure. ASTROPHYSICAL JOURNAL, 682(1), 68-80.
• Clowe, D., & Zaritsky, D. (2007). Shot in the dark. Physics World, 20(2), 26-29.
  More info

  Abstract: A cosmic collision between two galaxy clusters, known as the Bullet Cluster has provided researchers with evidences for the existence of dark matter. The forces involved in this event are so great that the X-ray emitting plasma is ripped away from the galaxy and any dark matter that might be present within them. The Bullet Cluster is valuable because the collision has separated the dominant baryonic component from the dominant dark matter. The scientists measured the shapes of very faint galaxies, taking care to only use those that were likely to be located behind the galaxy cluster and therefore lensed. A growing number of physicists have begun exploring methods to solve Zwicky's puzzle by developing alternative theories. Reserachers have analyzed that the strength of he Bullet Cluster lensing peaks compared with the total baryonic mass is similar to that of other clusters in which the stars and plasma are coincident.
• De, L. G., Poggianti, B. M., Aragon-Salamanca, A., White, S., Zaritsky, D., Clowe, D., Halliday, C., Jablonka, P., von, d., Milvang-Jensen, B., Pello, R., Rudnick, G., Saglia, R. P., & Simard, L. (2007). The build-up of the colour-magnitude relation in galaxy clusters z similar to 0.8. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 374(3), 809-822.
• Desai, V., Dalcanton, J. J., Aragón-Salamanca, A., Jablonka, P., Poggianti, B., Gogarten, S. M., Simard, L., Milvang-Jensen, B., Rudnick, G., Zaritsky, D., Clowe, D., Halliday, C., Pelló, R., Saglia, R., & White, S. (2007). The morphological content of 10 EDisCS clusters at 0.5 < z < 0.8 ^1,2. Astrophysical Journal, 660(2 I), 1151-1164.
  More info

  Abstract: We describe Hubble Space Telescope (HST) imaging of 10 of the 20 ESO Distant Cluster Survey (EDisCS) fields. Each ∼40 arcmin2 field was imaged in the F814W filter with the Advanced Camera for Surveys Wide Field Camera. Based on these data, we present visual morphological classifications for the ∼920 sources per field that are brighter than Iauto = 23 mag. We use these classifications to quantify the morphological content of 10 intermediate-redshift (0.5 < z < 0.8) galaxy clusters within the HST survey region. The EDisCS results, combined with previously published data from seven higher redshift clusters, show no statistically significant evidence for evolution in the mean fractions of elliptical, S0, and late-type (Sp+Irr) galaxies in clusters over the redshift range 0.5 < z < 1.2. In contrast, existing studies of lower redshift clusters have revealed a factor of ∼2 increase in the typical S0 fraction between z = 0.4 and 0, accompanied by a commensurate decrease in the Sp+Irr fraction and no evolution in the elliptical fraction. The EDisCS clusters demonstrate that cluster morphological fractions plateau beyond z ≈ 0.4. They also exhibit a mild correlation between morphological content and cluster velocity dispersion, highlighting the importance of careful sample selection in evaluating evolution. We discuss these findings in the context of a recently proposed scenario in which the fractions of passive (E, S0) and star-forming (Sp, Irr) galaxies are determined primarily by the growth history of clusters. © 2007. The American Astronomical Society. All rights reserved.
• Gonzalez, A. H., Clowe, D., Markevitchs, M., Randall, S., Bradact, M., Chung, S., Jones, C., & Zaritsky, D. (2007). The bullet cluster 130657-56: Implications for dark matter and galaxy evolution. Proceedings of the 6th International Workshop on the Identification of Dark Matter, IDM 2006, 128-134.
  More info

  Abstract: We present an overview of work on the merging cluster system 130657-56, commonly known as the "bullet" cluster. This system is one of only two known supersonic cluster mergers, and its unique properties enable fundamental constraints on the nature of dark matter. In a series of papers our group has used this system to demonstrate the existence of dark matter and place upper limits on the dark matter self-interaction cross section. In this proceedings we summarize these findings and discuss ongoing work to improve these constraints and quantify the impact of a supersonic merger on cluster galaxy evolution.
• Lucia, G. D., Poggianti, B. M., Aragón-Salamanca, A., D., S., Zaritsky, D., Clowe, D., Halliday, C., Jablonka, P., Von, A., Milvang-Jensen, B., Pelló, R., Rudnick, G., Saglia, R. P., & Simard, L. (2007). The build-up of the colour-magnitude relation in galaxy clusters since z ∼ 0.8. Monthly Notices of the Royal Astronomical Society, 374(3), 809-822.
  More info

  Abstract: Using galaxy clusters from the ESO Distant Cluster Survey, we study how the distribution of galaxies along the colour-magnitude relation has evolved since z ∼ 0.8. While red-sequence galaxies in all these clusters are well described by an old, passively evolving population, we confirm our previous finding of a significant evolution in their luminosity distribution as a function of redshift. When compared to galaxy clusters in the local Universe, the high-redshift EDisCS clusters exhibit a significant deficit of faint red galaxies. Combining clusters in three different redshift bins, and defining as 'faint' all galaxies in the range 0.4 ≳ L/L≳ 0.1, we find a clear decrease in the luminous-to-faint ratio of red galaxies from z ∼ 0.8 to ∼0.4. The amount of such a decrease appears to be in qualitative agreement with predictions of a model where the blue bright galaxies that populate the colour-magnitude diagram of high-redshift clusters, have their star formation suppressed by the hostile cluster environment. Although model results need to be interpreted with caution, our findings clearly indicate that the red-sequence population of high-redshift clusters does not contain all progenitors of nearby red-sequence cluster galaxies. A significant fraction of these must have moved on to the red sequence below z ∼ 0.8. © 2006 RAS.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2007). A Census of Baryons in Galaxy Clusters and Groups. The Astrophysical Journal, 666(1), 147-155. doi:10.1086/519729
  More info

  We determine the contribution of stars in galaxies, intracluster stars, and the intracluster medium to the total baryon budget in nearby galaxy clusters and groups. We find that the baryon mass fraction (fb ≡ Ωb/Ωm) within r500 is constant for systems with M500 between 6 × 1013 and 1 × 1015 M☉. Although fb is lower than the WMAP value, the shortfall is on the order of both the observational systematic uncertainties and the depletion of baryons within r500 that is predicted by simulations. The data therefore provide no compelling evidence for undetected baryonic components, particularly any that would be expected to vary in importance with cluster mass. A unique feature of the current analysis is direct inclusion of the contribution of intracluster light (ICL) in the baryon budget. With the addition of the ICL to the stellar mass in galaxies, the increase in X-ray gas mass fraction with increasing total mass is entirely accounted for by a decrease in the total stellar mass fraction, supporting the argument that the behavior of both the stellar and X-ray gas components is dominated by a decrease in star formation efficiency in more massive environments. Within just the stellar component, the fraction of the total stellar luminosity in the central, giant brightest cluster galaxy (BCG) and ICL (hereafter the BCG+ICL component) decreases as velocity dispersion (σ) increases for systems with 145 km s-1 ≤ σ ≤ 1026 km s-1, suggesting that the BCG+ICL component, and in particular the dominant ICL component, grows less efficiently in higher mass environments. The degree to which this behavior arises from our sample selection, which favored systems with central, giant elliptical galaxies, remains unclear. A more robust result is the identification of low-mass groups with large BCG+ICL components, demonstrating that the creation of "intracluster" stars does not require a massive cluster environment. Within r500 and r200, the BCG+ICL contributes on average 40% and 33% of the total stellar light, respectively, for the clusters and groups in our sample. Because these fractions are functions of both enclosed radius and system mass, care should be exercised when comparing these values with other studies and simulations.
• Zaritsky, D., & Christlein, D. (2007). On the extended knotted disks of galaxies. ASTRONOMICAL JOURNAL, 134(1), 135-141.
• Zaritsky, D., & Christlein, D. (2007). On the extended knotted disks of galaxies. Astronomical Journal, 134(1), 135-141.
  More info

  Abstract: The stellar disks of many spiral galaxies are twice as large as generally thought. We use archival data from the Galaxy Evolution Explorer mission to quantify the statistical properties of young stellar clusters in the outer, extended disks of a sample of 11 nearby galaxies. We find an excess of sources between 1.25 and 2 optical radii, R25, for five of the galaxies, which statistically implies that at least a quarter of such galaxies have this cluster population (90% confidence level), and no significant statistical excess in the sample as a whole beyond 2R25, even though one galaxy (M83) individually shows such an excess. Although the excess is typically most pronounced for blue (FUV -NUV < 1, NUV < 25) sources, there is also an excess of sources with redder colors. Although from galaxy to galaxy the number of sources varies significantly, on average the galaxies with such sources have 75 ± 10 blue sources at radii between 1.25R25 and 2R 25. In addition, the radial distribution is consistent with the extended dust emission observed in the far-IR and with the properties of Ha sources, assuming a constant cluster formation rate over the last few hundred megayears. All of these results suggest that the phenomenon of low-level star formation well outside the apparent optical edges of disks (R ∼ R 25) is common and long lasting. © 2007. The American Astronomical Society. All rights reserved.
• Zaritsky, D., Harris, J., & Thompson, . (2007). A digital photometric survey of the Magellanic Clouds: First results from one million stars. ASTRONOMICAL JOURNAL, 114(3), 1002-1013.
• Blum, R. D., Mould, J. R., Olsen, K. A., Frogel, J. A., Werner, M., Meixner, M., Markwick-Kemper, F., Indebetouw, R., Whitney, B., Meade, M., Babler, B., Churchwell, E. B., Gordon, K., Engelbracht, C., For, B. -., Misselt, K., Vijh, U., Leitherer, C., Volk, K., , Points, S., et al. (2006). Spitzer sage survey of the large magellanic cloud. II. Evolved stars and infrared color-magnitude diagrams. Astronomical Journal, 132(5), 2034-2045.
  More info

  Abstract: Color-magnitude diagrams (CMDs) are presented for the Spitzer SAGE (Surveying the Agents of a Galaxy's Evolution) survey of the Large Magellanic Cloud (LMC). IRAC and MIPS 24 μm epoch 1 data are presented. These data represent the deepest, widest mid-infrared CMDs of their kind ever produced in the LMC. Combined with the Two Micron All Sky Survey, the diagrams are used to delineate the evolved stellar populations in the LMC, as well as Galactic foreground and extragalactic background populations. Some 32,000 evolved stars brighter than the tip of the red giant branch are identified. Of these, approximately 17,500 are classified as oxygen-rich, 7000 as carbon-rich, and another 1200 as "extreme" asymptotic giant branch (AGB) stars. Brighter members of the latter group have been called "obscured" AGB stars in the literature owing to their dusty circumstellar envelopes. A large number (1200) of luminous oxygen-rich AGB stars/M supergiants are also identified. Finally, there is strong evidence from the 24 μm MIPS channel that previously unexplored, lower luminosity oxygen-rich AGB stars contribute significantly to the mass-loss budget of the LMC (1200 such sources are identified). © 2006. The American Astronomical Society. All rights reserved.
• Bradač, M., Clowe, D., Gonzalez, A. H., Marshall, P., Forman, W., Jones, C., Markevitch, M., Randall, S., Schrabback, T. I., & Zaritsky, D. (2006). Strong and weak lensing united. III. Measuring the mass distribution of the merging galaxy cluster 1ES 0657-558. Astrophysical Journal, 652(2 I), 937-947.
  More info

  Abstract: The galaxy cluster 1ES 0657-558 (z = 0.296) is remarkably well suited for addressing outstanding issues in both galaxy evolution and fundamental physics. We present a reconstruction of the mass distribution from both strong and weak gravitational lensing data. Multicolor, high-resolution HST ACS images allow detection of many more arc candidates than were previously known, especially around the subcluster. Using the known redshift of one of the multiply imaged systems, we determine the remaining source redshifts using the predictive power of the strong-lens model. Combining this information with shape measurements of "weakly" lensed sources, we derive a high-resolution, absolutely calibrated mass map, using no assumptions regarding the physical properties of the underlying cluster potential. This map provides the best available quantification of the total mass of the central part of the cluster. We also confirm the result from Clowe and colleagues that the total mass does not trace the baryonic mass. © 2006. The American Astronomical Society. All rights reserved.
• Clowe, D., Bradač, M., Gonzalez, A. H., Markevitech, M., Randall, S. W., Jones, C., & Zaritsky, D. (2006). A direct empirical proof of the existence of dark matter. Astrophysical Journal Letters, 648(2 II), L109-L113.
  More info

  Abstract: We present new weak-lensing observations of IE 0657-558 (z = 0.296), a unique cluster merger, that enable a direct detection of dark matter, independent of assumptions regarding the nature of the gravitational force law. Due to the collision of two clusters, the dissipationless stellar component and the fluid-like X-ray-emitting plasma are spatially segregated. By using both wide-field ground-based images and HST/ACS images of the cluster cores, we create gravitational lensing maps showing that the gravitational potential does not trace the plasma distribution, the dominant baryonic mass component, but rather approximately traces the distribution of galaxies. An 8 σ significance spatial offset of the center of the total mass from the center of the baryonic mass peaks cannot be explained with an alteration of the gravitational force law and thus proves that the majority of the matter in the system is unseen. © 2006. The American Astronomical Society. All rights reserved.
• Clowe, D., Schneider, P., Aragón-Salamanca, A., Bremer, M., Lucia, G. D., Halliday, C., Jablonka, P., Milvang-Jensen, B., Pelló, R., Poggianti, B., Rudnick, G., Saglia, R., Simard, L., White, S., & Zaritsky, D. (2006). Weak lensing mass reconstructions of the ESO Distant Cluster Survey. Astronomy and Astrophysics, 451(2), 395-408.
  More info

  Abstract: We present weak lensing mass reconstructions for the 20 high-redshift clusters in the ESO Distant Cluster Survey. The weak lensing analysis was performed on deep, 3-color optical images taken with VLT/FORS2, using a composite galaxy catalog with separate shape estimators measured in each passband. We find that the EDisCS sample is composed primarily of clusters that are less massive than those in current X-ray selected samples at similar redshifts, but that all of the fields are likely to contain massive clusters rather than superpositions of low mass groups. We find that 7 of the 20 fields have additional massive structures which are not associated with the clusters and which can affect the weak lensing mass determination. We compare the mass measurements of the remaining 13 clusters with luminosity measurements from cluster galaxies selected using photometric redshifts and find evidence of a dependence of the cluster mass-to-light ratio with redshift. Finally we determine the noise level in the shear measurements for the fields as a function of exposure time and seeing and demonstrate that future ground-based surveys which plan to perform deep optical imaging for use in weak lensing measurements must achieve point-spread functions smaller than a median of 0.″ 6 FWHM. © ESO 2006.
• Halliday, C., Milvang-Jensen, B., Poirier, S., Poggianti, B., Jablonka, P., Aragon-Salamanca, A., Saglia, R., De Lucia, G., Pello, R., Simard, L., Clowe, D., Rudnick, G., Dalcanton, J., White, S., & Zaritsky, D. (2006). Spectroscopy of clusters in the ESO Distant Cluster Survey (EDisCS) - Redshifts, velocity dispersions and substructure for 5 clusters. ASTRONOMY & ASTROPHYSICS, 427(2), 397-413.
• Harris, J., & Zaritsky, D. (2006). Spectroscopic survey of red giants in the small magellanic cloud. I. Kinematics. Astronomical Journal, 131(5), 2514-2524.
  More info

  Abstract: We present a spectroscopic survey of 2046 red giant stars, distributed over the central 4 kpc × 2 kpc of the Small Magellanic Cloud (SMC). After fitting and removing a small velocity gradient across the SMC (8.3 km s -1 deg -1 oriented at 23°.4 east of north), we measure an rms velocity scatter of 27.5 ± 0.5 km s -1. The line-of-sight velocity distribution is well-characterized by a Gaussian, and the velocity dispersion profile is nearly constant as a function of radius. We find no kinematic evidence of tidal disturbances. Without a high-precision measurement of the SMC's proper motion, it is not possible to constrain its true rotation speed from our measured radial velocity gradient. However, even with conservative assumptions, we find that ν < σ, and hence that the SMC is primarily supported by its velocity dispersion. We find that the shape of the SMC, as measured from the analysis of the spatial distribution of its red giant stars, is consistent with the degree of rotational flattening expected for the range of allowed νi/σ values. As such, the properties of the SMC are consistent with similar low-luminosity spheroidal systems. We conclude that the SMC is primarily a low-luminosity spheroid whose irregular visual appearance is dominated by recent star formation. A simple virial analysis using the measured kinematics implies an enclosed mass within 1.6 kpc of between 1.4 and 1.9 × 10 9M ⊙ and a less well-constrained mass within 3 kpc of between 2.7 and 5.1 × 10 9 M ⊙. © 2006. The American Astronomical Society. All rights reserved.
• Herbert-Fort, S., Zaritsky, D., Kim, Y. J., Bailin, J., & Taylor, J. E. (2006). Rotation of galaxy dark matter halos. Proceedings of the International Astronomical Union, 2(S235), 104-.
  More info

  Abstract: The degree to which outer dark matter halos of spiral galaxies rotate with the disk is sensitive to their accretion history and may be probed with associated satellite galaxies. We use the Steward Observatory Bok telescope to measure the sense of rotation of nearby isolated spirals and combine these data with those of their associated satellites (drawn from SDSS) to directly test predictions from numerical simulations. We aim to constrain models of galaxy formation by measuring the projected component of the halo angular momentum that is aligned with that of spiral galaxy disks, Jz. We find the mean bulk rotation of the ensemble satellite system to be co-rotating with the disk with a velocity of 22 13 km/s, in general agreement with previous observational studies and suggesting that galaxy disks could be formed by halo baryons collapsing by a factor of 10. We also find a prograde satellite fraction of 51% and Jz, of the satellite system to be positively correlated with the disk, albeit at low significance (2655 2232 kpc km/s). © 2007 International Astronomical Union.
• Hill, A., & Zaritsky, D. (2006). The star clusters of the small magellanic cloud: Structural parameters. Astronomical Journal, 131(1), 414-430.
  More info

  Abstract: We present structural parameters for 204 stellar clusters in the Small Magellanic Cloud derived from fitting King and Elson, Fall, and Freeman (EFF) model profiles to the F-band surface brightness profiles as measured from the Magellanic Clouds Photometric Survey images. Both King and EFF profiles are satisfactory fits to the majority of the profiles, although King profiles are generally slightly superior to the softened power-law profiles of EFF and provide statistically acceptable fits to ∼90% of the sample. We find no correlation between the preferred model and cluster age. The only systematic deviation in the surface brightness profiles that we identify is a lack of a central concentration in a subsample of clusters, which we designate as "ring" clusters. In agreement with previous studies, we find that the clusters in the SMC are significantly more elliptical than those in the Milky Way. However, given the mean age difference and the rapid destruction of these systems, the comparison between the SMC and the Milky Way should not directly be interpreted as a difference in either the initial cluster properties or their subsequent evolution. We find that cluster ellipticity correlates with cluster mass more strongly than with cluster age. We identify several other correlations (central surface brightness vs. local background density, core radius vs. tidal force, and size vs. distance) that can be used to constrain models of cluster evolution in the SMC. © 2006. The American Astronomical Society. All rights reserved.
• Hunsberger, S., Charlton, J., & Zaritsky, D. (2006). The formation of dwarf galaxies in tidal debris: A study of the compact group environment. ASTROPHYSICAL JOURNAL, 462(1), 50-+.
• Johnson, O., Best, P., Zaritsky, D., Clowe, D., Aragón-Salamanca, A., Halliday, C., Jablonka, P., Milvang-Jensen, B., Pelló, R., Poggianti, B. M., Rudnick, G., Saglia, R., Simard, L., & White, S. (2006). The X-ray properties of optically selected z > 0.6 clusters in the European Southern Observatory Distant Cluster Survey. Monthly Notices of the Royal Astronomical Society, 371(4), 1777-1792.
  More info

  Abstract: We present XMM-Newton observations of three optically selected z > 0.6 clusters from the European Southern Observatory (ESO) Distant Cluster Survey (EDisCS), comprising the first results of a planned X-ray survey of the full EDisCS high-redshift sample. The EDisCS clusters were identified in the Las Campanas Distant Cluster Survey as surface brightness fluctuations in the optical sky and their masses and galaxy populations are well described by extensive photometric and spectroscopic observations. We detect two of the three clusters in the X-ray and place a firm upper limit on diffuse emission in the third cluster field. We are able to constrain the X-ray luminosity and temperature of the detected clusters and estimate their masses. We find that the X-ray properties of the detected EDisCS clusters are similar to those of X-ray-selected clusters of comparable mass and - unlike other high-redshift, optically selected clusters - are consistent with the T-σ and L X-σ relations determined from X-ray-selected clusters at low redshift. The X-ray determined mass estimates are generally consistent with those derived from weak-lensing and spectroscopic analyses. These preliminary results suggest that the novel method of optical selection used to construct the EDisCS catalogue may, like selection by X-ray luminosity, be well suited for identification of relaxed, high-redshift clusters whose intracluster medium is in place and stable by z ∼ 0.8. © 2006 RAS.
• Meixner, M., Gordon, K. D., Indebetouw, R., Hora, J. L., Whitney, B., Blum, R., Reach, W., Bernard, J., Meade, M., Babler, B., Engelbracht, C. W., For, B., Misselt, K., Vijh, U., Leitherer, C., Cohen, M., Churchwell, E. B., Boulanger, F., Frogel, J. A., , Fukui, Y., et al. (2006). Spitzer survey of the Large Magellanic Cloud: Surveying the agents of a galaxy's evolution (sage). I. Overview and initial results. ASTRONOMICAL JOURNAL, 132(6), 2268-2288.
• Meixner, M., Gordon, K. D., Indebetouw, R., Hora, J. L., Whitney, B., Blum, R., Reach, W., Bernard, J., Meade, M., Babler, B., Engelbracht, C. W., For, B., Misselt, K., Vijh, U., Leitherer, C., Cohen, M., Churchwell, E. B., Boulanger, F., Frogel, J. A., , Fukui, Y., et al. (2006). Spitzer survey of the large magellanic cloud: Surveying the agents of a Galaxy's evolution (SAGE). I. Overview and initial results. Astronomical Journal, 132(6), 2268-2288.
  More info

  Abstract: We are performing a uniform and unbiased imaging survey of the Large Magellanic Cloud (LMC; ∼7° × 7°) using the IRAC (3.6,4.5, 5.8, and 8 μm) and MIPS (24, 70, and 160 μm) instruments on board the Spitzer Space Telescope in the Surveying the Agents of a Galaxy's Evolution (SAGE) survey, these agents being the interstellar medium (ISM) and stars in the LMC. This paper provides an overview of the SAGE Legacy project, including observing strategy, data processing, and initial results. Three key science goals determined the coverage and depth of the survey. The detection of diffuse ISM with column densities > 1.2 × 1021 Hcm-2 permits detailed studies of dust processes in the ISM. SAGE's point-source sensitivity enables a complete census of newly formed stars with masses >3 M ⊙ that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass-loss rates >1 × 10-8 M⊙ yr-1 will quantify the rate at which evolved stars inject mass into the ISM of the LMC. The observing strategy includes two epochs in 2005, separated by 3 months, that both mitigate instrumental artifacts and constrain source variability. The SAGE data are nonproprietary. The data processing includes IRAC and MIPS pipelines and a database for mining the point-source catalogs, which will be released to the community in support of Spitzer proposal cycles 4 and 5. We present initial results on the epoch 1 data for a region near N79 and N83. The MIPS 70 and 160 μm images of the diffuse dust emission of the N79/N83 region reveal a similar distribution to the gas emissions, especially the H I 21 cm emission. The measured point-source sensitivity for the epoch 1 data is consistent with expectations for the survey. The point-source counts are highest for the IRAC 3.6 μm band and decrease dramatically toward longer wavelengths, consistent with the fact that stars dominate the point-source catalogs and the dusty objects detected at the longer wavelengths are rare in comparison. The SAGE epoch 1 point-source catalog has ∼4 × 106 sources, and more are anticipated when the epoch 1 and 2 data are combined. Using Milky Way (MW) templates as a guide, we adopt a simplified point-source classification to identify three candidate groups - stars without dust, dusty evolved stars, and young stellar objects-that offer a starting point for this work. We outline a strategy for identifying foreground MW stars, which may comprise as much as 18% of the source list, and background galaxies, which may comprise ∼12% of the source list. © 2006, The American Astronomical Society, All rights reserved.
• Pogianti, B. M., Von, A., Lucia, G. D., Desai, V., Simard, L., Halliday, C., Aragón-Salamanca, A., Bower, R., Varela, J., Best, P., Clowe, D. I., Dalcanton, J., Jablonka, P., Milvang-Jensen, B., Pello, R., Rudnick, G., Saglia, R., D., S., & Zaritsky, D. (2006). The evolution of the star formation activity in galaxies and its dependence on environment. Astrophysical Journal Letters, 642(1 I), 188-215.
  More info

  Abstract: We study how the proportion of star-forming galaxies evolves between z = 0.8 and 0 as a function of galaxy environment, using the O II line in emission as a signature of ongoing star formation. Our high-z data set comprises 16 clusters, 10 groups, and another 250 galaxies in poorer groups and the field at z = 0.4-0.8 from the ESO Distant Cluster Survey, plus another 9 massive clusters at similar redshifts. As a local comparison, we use galaxy systems selected from the Sloan Digital Sky Survey (SDSS) at 0.04 < z < 0.08. At high z most systems follow a broad anticorrelation between the fraction of star-forming galaxies and the system velocity dispersion. At face value, this suggests that at z = 0.4-0.8 the mass of the system largely determines the proportion of galaxies with ongoing star formation. At these redshifts the strength of star formation (as measured by the O II equivalent width) in star-forming galaxies is also found to vary systematically with environment. SDSS clusters have much lower fractions of starforming galaxies than clusters at z = 0.4-0.8 and, in contrast with the distant clusters, show a plateau for velocity dispersions ≥550 km s-1, where the fraction of galaxies with O II emission does not vary systematically with velocity dispersion. We quantify the evolution of the proportion of star-forming galaxies as a function of the system velocity dispersion and find that it is strongest in intermediate-mass systems (σ ∼ 500-600 km s-1 at z = 0). To understand the origin of the observed trends, we use the Press-Schechter formalism and the Millennium Simulation and show that galaxy star formation histories may be closely related to the growth history of clusters and groups. If the scenario we propose is roughly correct, the link between galaxy properties and environment is extremely simple to predict purely from a knowledge of the growth of dark matter structures. © 2006, The American Astronomical Society. All rights reserved.
• RIX, H., & ZARITSKY, D. (2006). NONAXISYMMETRIC STRUCTURES IN THE STELLAR DISKS OF GALAXIES. ASTROPHYSICAL JOURNAL, 447(1), 82-102.
• Yang, Y., Tremonti, C. A., Zabludoff, A. I., & Zaritsky, D. (2006). E+A galaxies with blue cores: Active galaxies in transition. ASTROPHYSICAL JOURNAL, 646(1), L33-L36.
• ZARITSKY, D., & LO, K. (2006). EVIDENCE FOR NONAXISYMMETRIC NUCLEAR BULGES IN SPIRAL GALAXIES. ASTROPHYSICAL JOURNAL, 303(1), 66-75.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2006). Local Group Dwarf Galaxies and the Fundamental Manifold of Spheroids. The Astrophysical Journal, 642(1), L37-L40. doi:10.1086/504352
  More info

  The fundamental manifold (FM), an extension of the fundamental plane formalism, incorporates all spheroid-dominated stellar systems from dwarf ellipticals up to the intracluster stellar populations of galaxy clusters by accounting for the continuous variation of the mass-to-light ratio within the effective radius re with scale. Here we find that Local Group dwarf spheroidal and dwarf elliptical galaxies, which probe the FM relationship roughly one decade lower in re than previous work, lie on the extrapolation of the FM. When combined with the earlier data, these Local Group dwarfs demonstrate the validity of the empirical manifold over nearly 4 orders of magnitude in re. The continuity of the galaxy locus on the manifold and, more specifically, the overlap on the FM of dwarf ellipticals like M32 and dwarf spheroidals like Leo II, imply that dwarf spheroidals belong to the same family of spheroids as their more massive counterparts. The only significant outliers are Ursa Minor and Draco. We explore whether the deviation of these two galaxies from the manifold reflects a breakdown in the coherence of the empirical relationship at low luminosities or rather the individual dynamical peculiarities of these two objects. We discuss some implications of our results for how the lowest mass galaxies form.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2006). The fundamental manifold of spheroids. The Astrophysical Journal, 638(2), 725-738. doi:10.1086/498672
  More info

  We present a unifying empirical description of the structural and kinematic properties of all spheroids embedded in dark matter halos. We find that the intracluster stellar spheroidal components of galaxy clusters, which we call cluster spheroids (CSphs) and which are typically 100 times the size of normal elliptical galaxies, lie on a "fundamental plane" as tight as that defined by elliptical galaxies (rms in effective radius of ~0.07) but having a different slope. The slope, as measured by the coefficient of the log σ term, declines significantly and systematically between the fundamental planes of ellipticals, brightest cluster galaxies (BCGs), and CSphs. We attribute this decline primarily to a continuous change in Me/Le, the mass-to-light ratio within the effective radius re, with spheroid scale. The magnitude of the slope change requires that it arise principally from differences in the relative distributions of luminous and dark matter, rather than from stellar population differences such as in age and metallicity. By expressing the Me/Le term as a function of σ in the simple derivation of the fundamental plane and requiring the behavior of that term to mimic the observed nonlinear relationship between log Me/Le and log σ, we simultaneously fit a two-dimensional manifold to the measured properties of dwarf elliptical and elliptical galaxies, BCGs, and CSphs. The combined data have an rms scatter in log re of 0.114 (0.099 for the combination of ellipticals, BCGs, and CSphs), which is modestly larger than each fundamental plane has alone, but which includes the scatter introduced by merging different studies done in different filters by different investigators. This "fundamental manifold" fits the structural and kinematic properties of spheroids that span a factor of 100 in σ and 1000 in re. While our mathematical form is neither unique nor derived from physical principles, the tightness of the fit leaves little room for improvement by other unification schemes over the range of observed spheroids.
• Zaritsky, D. (2006). Dust and stellar populations in the Large Magellanic Cloud. ASTRONOMICAL JOURNAL, 118(6), 2824-2838.
• Zaritsky, D., Harris, J., Thompson, I., & Grebel, E. (2006). The Magellanic Clouds photometric survey: The Large Magellanic Cloud stellar catalog and extinction map. ASTRONOMICAL JOURNAL, 128(4), 1606-1614.
• Balogh, M., Christlein, D., Zabludoff, A., & Zaritsky, D. (2005). The environmental dependence of the infrared luminosity and stellar mass functions. ASTROPHYSICAL JOURNAL, 557(1), 117-125.
• Bradac, M., Clowe, D., Gonzalez, A. H., Marshall, P., Forman, W., Jones, C., Markevitch, M., Randall, S., Schrabback, T., & Zaritsky, D. (2005). Strong and weak lensing united. III. Measuring the mass distribution of the merging galaxy cluster 1ES 0657-558. ASTROPHYSICAL JOURNAL, 652(2), 937-947.
• Gonzalez, A. H., Tran, K. H., Conbere, M. N., & Zaritsky, D. (2005). Galaxy cluster assembly at z = 0.37. Astrophysical Journal Letters, 624(2 II), L73-L76.
  More info

  Abstract: We present X-ray and spectroscopic confirmation of a cluster assembling from multiple, distinct galaxy groups at z = 0.371. Initially detected in the Las Campanas Distant Cluster Survey, the structure contains at least four X-ray-detected groups that lie within a maximum projected separation of 4 Mpc and within Δv = 550 km s-1 of one another. Using Chandra imaging and wide-field optical spectroscopy, we show that the individual groups lie on the local σ-T relation and derive a total mass of M ≥ 5 × 1014 M⊙ for the entire structure. We demonstrate that the groups are gravitationally bound to one another and will merge into a single cluster with about one-third or more the mass of Coma. We also find that although the cluster is in the process of forming, the individual groups already have a higher fraction of passive members than the field. This result indicates that galaxy evolution on group scales is key to developing the early-type galaxies that dominate the cluster population by z ∼ 0. © 2005. The American Astronomical Society. All rights reserved.
• Gonzalez, A., Zaritsky, D., Dalcanton, J., & Nelson, A. (2005). The Las Campanas Distant Cluster Survey: The catalog. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 137(1), 117-138.
• Mccarthy, D. W., Zaritsky, D., Simard, L., Rudnick, G., Poggianti, B. M., Pello, R., Milvang-jensen, B., Mccarthy, J. D., Mccarthy, D. W., Halliday, C., & Finn, R. A. (2005). Hα-derived Star Formation Rates for Three z≃0.75 EDisCS Galaxy Clusters* **. The Astrophysical Journal, 630(1), 206-227. doi:10.1086/431642
  More info

  We present H®-derived star-formation rates (SFRs) for three z ' 0.75 galaxy clusters. Our 1¾ flux limit corresponds to a star-formation rate of 0.10-0.24 h i2 100 Myr i1 , and our minimum reliable H® + (N II) rest-frame equivalent width is 10 u We show that H® narrowband imaging is an efficient method for measuring star formation in distant clusters. In two out of three clusters, we find that the fraction of star-forming galaxies increases with projected distance from the cluster center. We also find that the fraction of star-forming galaxies decreases with increasing local galaxy surface density in the same two clusters. We compare the median rate of star formation among star-forming cluster galaxies to a small sample of star-forming field galaxies from the literature and find that the median cluster SFRs are » 50% less than the median field SFR. We characterize cluster evolution in terms of the mass-normalized integrated cluster SFR and find that the z ' 0.75 clusters have more SFR per cluster mass on average than the z · 0.4 clusters from the literature. The interpretation of this result is complicated by the dependence of the mass-normalized SFR on cluster mass and the lack of sufficient overlap in the mass ranges covered by the low and high redshift samples. We find that the fraction and luminosities of the brightest starburst galaxies at z ' 0.75 are consistent with their being progenitors of the post-starburst galaxies at z ' 0.45 if the post-starburst phase lasts several (» 5) times longer than the starburst phase. Subject headings: galaxies: clusters: general — galaxies: high-redshift — stars: formation — galaxies: evolution
• Rafelski, M., & Zaritsky, D. (2005). The star clusters of the small magellanic cloud: Age distribution. Astronomical Journal, 129(6), 2701-2713.
  More info

  Abstract: We present age measurements for 195 star clusters in the Small Magellanic Cloud based on comparison of integrated colors measured from the Magellanic Clouds Photometric Survey with models of simple stellar populations. We find that the modeled nonuniform changes of cluster colors with age can lead to spurious age peaks in the cluster age distribution; that the observed numbers of clusters with age t declines smoothly as t -2.1; that for an assumed initial cluster mass function scaling as M -2, the dependence of the cluster disruption time on mass is proportional to M 0.48; that despite the apparent abundance of young clusters, the dominant epoch of cluster formation was the initial one; and that there are significant differences in the spatial distribution of clusters of different ages. Because of limited precision in our age measurements, we cannot address the question of detailed correspondence between the cluster age function and the field star formation history. However, this sample provides an initial guide as to which clusters to target in more detailed studies of specific age intervals. © 2005. The American Astronomical Society. All rights reserved.
• White, S. D., Clowe, D. I., Simard, L., Rudnick, G., Lucia, G. D., Aragón-Salamanca, A., Bender, R., Best, P., Bremer, M., Charlot, S., Dalcanton, J., Dantel, M., Desai, V., Fort, B., Halliday, C., Jablonka, P., Kauffmann, G., Mellier, Y., Milvang-Jensen, B., , Pelló, R., et al. (2005). EDisCS - The ESO distant cluster survey. Sample definition and optical photometry. Astronomy and Astrophysics, 444(2), 365-379.
  More info

  Abstract: We present the ESO Distant Cluster Survey (EDisCS), a survey of 20 fields containing distant galaxy clusters with redshifts ranging from 0.4 to almost 1.0. Candidate clusters were chosen from among the brightest objects identified in the Las Campanas Distant Cluster Survey, half with estimated redshift z est ∼0.5 and half with zest ∼0.8. They were confirmed by identifying red sequences in moderately deep two colour data from VLT/FORS2. For confirmed candidates we have assembled deep three-band optical photometry using VLT/FORS2, deep near-infrared photometry in one or two bands using NTT/SOFI, deep optical spectroscopy using VLT/FORS2, wide field imaging in two or three bands using the ESO Wide Field Imager, and HST/ACS mosaic images for 10 of the most distant clusters. This first paper presents our sample and the VLT photometry we have obtained. We present images, colour-magnitude diagrams and richness estimates for our clusters, as well as giving redshifts and positions for the brightest cluster members. Subsequent papers will present our infrared photometry, spectroscopy, HST and wide-field imaging, as well as a wealth of further analysis and science results. Our reduced data become publicly available as these papers are accepted. © ESO 2005.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2005). Intracluster Light in Nearby Galaxy Clusters: Relationship to the Halos of Brightest Cluster Galaxies. The Astrophysical Journal, 618(1), 195-213. doi:10.1086/425896
  More info

  We present a detailed analysis of the surface brightness distribution of the brightest cluster galaxy (BCG) in each of 24 galaxy clusters at 0.03 < z < 0.13. We use two-dimensional profile fitting to model the surface brightness out to r = 300 kpc for each BCG, comparing r1/4, r1/n, and double r1/4 models. We obtain statistically superior fits using a two-component model consisting of a pair of r1/4 profiles with independent scale lengths, ellipticities, and orientations. The two-component model can simply reproduce the observed position angle and ellipticity gradients, which cannot generally be explained purely by triaxiality. The inner component of our two-component model has properties similar to those of a typical massive elliptical galaxy and is clearly associated with the BCG. The outer component is 10-40 times larger in scale, has ~10 times the total luminosity of the inner component, and exhibits a steeper μ-re relation than that of the elliptical fundamental plane. We interpret this outer component as a population of intracluster stars that trace the cluster potential. The two components are strongly aligned (|Δθ| < 10°) in roughly 40% of the clusters. When they are not aligned, the components tend toward high degrees of misalignment, suggesting that accretion of infalling material may change the orientation of some BCGs for a time. The extent of the outer component and its similar elongation to published cluster galaxy distributions indicates that the evolution of the intracluster light is tied to the cluster as a whole rather than to the BCG.
• Zaritsky, D., Gonzalez, A., & Zabludoff, A. (2005). The fundamental manifold of spheroids. ASTROPHYSICAL JOURNAL, 638(2), 725-738.
• Halliday, C., Milvang-Jensen, B., Poirier, S., Poggianti, B. M., Jablonka, P., Aragón-Salamanca, A., Saglia, R. P., Lucia, G. D., Pelló, R., Simard, L., Clowe, D. I., Rudnick, G., Dalcanton, J. J., White, S. D., & Zaritsky, D. (2004). Spectroscopy of clusters in the ESO Distant Cluster Survey (EDisCS) Redshifts, velocity dispersions and substructure for 5 clusters. Astronomy and Astrophysics, 427(2), 397-413.
  More info

  Abstract: We present spectroscopic observations of galaxies in 4 clusters at z = 0.7-0.8 and in one cluster at z ∼ 0.5 obtained with the FORS2 spectrograph on the VLT as part of the ESO Distant Cluster Survey (EDisCS), a photometric and spectroscopic survey of 20 intermediate to high redshift clusters. We describe our target selection, mask design, observation and data reduction procedures, using these first 5 clusters to demonstrate how our strategies maximise the number of cluster members for which we obtain spectroscopy. We present catalogues containing positions, I-band magnitudes and spectroscopic redshifts for galaxies in the fields of our 5 clusters. These contain 236 cluster members, with the number of members per cluster ranging from 30 to 67. Our spectroscopic success rate, i.e. the fraction of spectroscopic targets which are cluster members, averages 50% and ranges from 30% to 75%. We use a robust biweight estimator to measure cluster velocity dispersions from our spectroscopic redshift samples. We also make a first assessment of substructure within our clusters. The velocity dispersions range from 400 to 1100 km s-1. Some of the redshift distributions are significantly non-Gaussian and we find evidence for significant substructure in two clusters, one at z ∼ 0.79 and the other at z ∼ 0.54. Both have velocity dispersions exceeding 1000 kms-1 but are clearly not fully virialised; their velocity dispersions may thus be a poor indicator of their masses. The properties of these first 5 EDisCS clusters span a wide range in redshift, velocity dispersion, richness and substructure, but are representative of the sample as a whole. Spectroscopy for the full dataset will allow a comprehensive study of galaxy evolution as a function of cluster environment and redshift.
• Harris, J., & Zaritsky, D. (2004). Spectroscopic survey of red giants in the Small Magellanic Cloud. I. Kinematics. ASTRONOMICAL JOURNAL, 131(5), 2514-2524.
• Harris, J., & Zaritsky, D. (2004). The star formation history of the small magellanic cloud. Astronomical Journal, 127(3 1779), 1531-1544.
  More info

  Abstract: We present the spatially resolved star formation and chemical enrichment history of the Small Magellanic Cloud (SMC) across the entire central 4° × 4°.5 area of the main body, based on UBVI photometry from our Magellanic Clouds Photometric Survey. We find that (1) approximately 50% of the stars that ever formed in the SMC formed prior to 8.4 Gyr ago (z > 1.2 for WMAP cosmology); (2) the SMC formed relatively few stars between 8.4 and 3 Gyr ago; (3) there was a rise in the mean star formation rate during the most recent 3 Gyr punctuated by "bursts" at ages of 2.5, 0.4, and 0.06 Gyr; (4) the bursts at 2.5 and 0.4 Gyr are temporally coincident with past perigalactic passages of the SMC with the Milky Way; (5) there is preliminary evidence for a large-scale annular structure in the 2.5 Gyr burst; and (6) the chemical enrichment history derived from our analysis is in agreement with the age-metalliciry relation of the SMC's star clusters. Consistent interpretation of the data required an ad hoc correction of 0.1-0.2 mag to the B-V colors of 25% of the stars; the cause of this anomaly is unknown, but we show that it does not strongly influence our results.
• Mccarthy, D. W., Zaritsky, D., Mccarthy, J. D., Mccarthy, D. W., & Finn, R. A. (2004). Hα-derived Star Formation Rates for the z = 0.84 Galaxy Cluster Cl J0023+0423B* **. The Astrophysical Journal, 604(1), 141-152. doi:10.1086/381729
  More info

  We present Hα-derived star formation rates (SFRs) for the galaxy cluster Cl J0023+0423B at z = 0.845. Our 3 σ flux limits correspond to an SFR of 0.24 h M☉ yr-1, and our minimum reliable Hα + [N ] equivalent width is greater than 10 A, demonstrating that near-infrared narrowband imaging can sample the star-forming galaxy population in distant clusters. Comparison with spectroscopy shows that the number of false detections is low (9% ± 6%) and that our Hα equivalent widths are correlated with spectroscopically determined [O II] equivalent widths. A magnitude-limited spectroscopic survey conducted over the same area missed 70% of the star-forming galaxies and 65% of the integrated star formation. Using Hubble Space Telescope Wide Field Planetary Camera 2 Archive images, we fit Sersic profiles to all galaxies with significant narrowband equivalent widths and find that equivalent width decreases as the steepness of galaxy profile increases. We find no significant population of early-type galaxies with ongoing star formation. The integrated SFR per cluster mass of Cl J0023+0423B is a factor of 10 higher than that of the three z ~ 0.2 clusters in the literature with available Hα observations. A larger sample of z ~ 0.8 clusters spanning a range of cluster masses is needed to determine whether this variation is due to a difference in cluster mass or redshift.
• Rafelski, M., & Zaritsky, D. (2004). The star clusters of the small Magellanic Cloud: Age distribution. ASTRONOMICAL JOURNAL, 129(6), 2701-2713.
• Rudnick, G., Schneider, P., Zaritsky, D., White, S. D., Simard, L., Schneider, P., Saglia, R. P., Rudnick, G., Rottgering, H., Poirier, S., Poggianti, B. M., Pello, R., Milvang-jensen, B., Mellier, Y., Lucia, G. D., Kauffmann, G., Jablonka, P., Halliday, C., Fort, B., , Desai, V., et al. (2004). Studying galaxy cluster evolution with the ESO distant cluster survey. Bulletin of the American Astronomical Society.
• Yang, Y., Zabludoff, A. I., Zaritsky, D., & Mihos, J. C. (2004). THE DETAILED EVOLUTION OF E plus A GALAXIES INTO EARLY TYPES. ASTROPHYSICAL JOURNAL, 688(2), 945-971.
• ZARITSKY, D., & WHITE, S. (2004). THE MASSIVE HALOS OF SPIRAL GALAXIES. ASTROPHYSICAL JOURNAL, 435(2), 599-610.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2004). Intracluster stars and the chemical enrichment of the intracluster medium. The Astrophysical Journal, 613(2), L93-L96. doi:10.1086/425253
  More info

  We explore the contribution of intracluster stars (ICS) to the chemical enrichment history of the intracluster medium (ICM). In contrast to scenarios in which all the metals originate in cluster galaxies and are then transported into the ICM, ICS enrich the ICM in situ, thereby contributing 100% of their supernovae ejecta directly into the ICM. Modeling the ICS as an ancient single-burst stellar population with a normal initial mass function, we generate ICM iron abundances in the range of the observed values of several tenths solar. Large observational and theoretical uncertainties preclude us from concluding that the ICS are the primary contributor of metals to the ICM in general. However, for the two clusters in our sample and one from the literature, for which all of the required observational constraints exist, we are able to reproduce between half and all of the ICM iron with this simple model. Because of the ubiquity of ICS in clusters and their direct connection with the ICM, we conclude that all models of the chemical enrichment history and energy budget of the ICM should account for the impact of the ICS.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., Yang, Y., Mihos, J. C., & Lauer, T. R. (2004). E+A Galaxies and the Formation of Early-Type Galaxies at z~0. The Astrophysical Journal, 607(1), 258-273. doi:10.1086/383259
  More info

  E+A galaxies, whose spectra have deep Balmer absorption lines but no significant [O II] emission, are the best candidates for an evolutionary link between star-forming, gas-rich galaxies and quiescent, gas-poor galaxies. However, their current morphologies are not well known. We present Hubble Space Telescope WFPC2 observations of the five bluest E+A galaxies (z ~ 0.1) in the sample of Zabludoff and coworkers to study whether their detailed morphologies are consistent with late- to early-type evolution and to determine what drives that evolution. The morphologies of four galaxies are disturbed, indicating that a galaxy-galaxy merger is at least one mechanism that leads to the E+A phase. Two-dimensional image fitting shows that the E+As are generally bulge-dominated systems, even though at least two E+As may have underlying disks. In the fundamental plane, E+As stand apart from the E/S0 galaxies mainly because of their high effective surface brightness. Fading of the young stellar population and the corresponding increase in their effective radii will cause these galaxies to migrate toward the locus of E/S0 galaxies. E+As have profiles qualitatively like those of normal power-law early-type galaxies but have higher surface brightnesses. This result provides the first direct evidence supporting the hypothesis that power-law elliptical galaxies form via gas-rich mergers. In total, at least four E+As are morphologically consistent with early-type galaxies. We detect compact sources, possibly young star clusters, associated with the galaxies. These sources are much brighter (MR ~ -13) than Galactic globular clusters, have luminosities consistent with the brightest clusters in nearby starburst galaxies, and have blue colors consistent with the ages estimated from the E+A galaxy spectra (several 108 yr). Further study of such young star cluster candidates might provide the elusive chronometer needed to break the age/burst-strength degeneracy for these postmerger galaxies.
• Zaritsky, D. (2004). The case of the off-center, levitating bar in the large magellanic cloud. Astrophysical Journal Letters, 614(1 II), L37-L40.
  More info

  Abstract: I explore the hypothesis that many of the unusual aspects of the apparent stellar bar of the Large Magellanic Cloud (LMC) are the result of viewing a triaxial stellar bulge that is embedded in a highly obscuring thin disk. Specifically, this hypothesis explains the observed off-center position of the bar within the disk, the differing apparent distances of the bar and disk, the near alignment of the bar's major-axis position angle and the disk's line of nodes, and the asymmetric appearance of the bar itself. Indirectly, it may also play a role in explaining the microlensing rate toward the LMC and the recently observed large velocity dispersion of RR Lyrae stars.
• Zaritsky, D., & Harris, J. (2004). Quantifying the drivers of star formation on galactic scales. I. The Small Magellanic Cloud. ASTROPHYSICAL JOURNAL, 604(1), 167-175.
• Zaritsky, D., & Harris, J. (2004). Quantifying the drivers of star formation on galactic scales. I. The Small Magellanic Cloud. Astrophysical Journal Letters, 604(1 I), 167-175.
  More info

  Abstract: We use the star formation history of the Small Magellanic Cloud (SMC) to place quantitative limits on the effect of tidal interactions and gas infall on the star formation and chemical enrichment history of the SMC. The coincident timing of two recent (10%, and could be as large as 70%.
• Zaritsky, D., Harris, J., Thompson, I. B., & Grebel, E. K. (2004). The Magellanic Clouds photometric survey: The Large Magellanic Cloud stellar catalog and extinction map. Astronomical Journal, 128(4), 1606-1614.
  More info

  Abstract: We present our catalog of U, B, V, and I stellar photometry of the central 64 deg 2 area of the Large Magellanic Cloud. Internal and external astrometric and photometric tests using existing optical photometry (U, B, and V from Massey's bright star catalog and I from the near-infrared sky survey DENIS) are used to confirm our observational uncertainty estimates. We fit stellar atmosphere models to the optical data to check the consistency of the photometry for individual stars across the passbands and to estimate the line-of-sight extinction. Finally, we use the estimated line-of-sight extinctions to produce an extinction map across the Large Magellanic Cloud, confirm the variation of extinction as a function of stellar population, and produce a simple geometric model for the extinction as a function of stellar population.
• Bolte, M., Calkins, M. L., Challis, P., Impey, C., Jannuzi, B. T., Jha, S., Miller, L. R., Olszewski, E. W., Zaritsky, D., Zaritsky, D., Windhorst, R. A., Weisz, D. R., Thompson, I. B., Thomas-osip, J. E., Stanek, K. Z., Spahr, T., Schweiker, H., Schild, R. E., Sasselov, D. D., , Pindor, B., et al. (2003). Photometry and Spectroscopy of GRB 030329 and its Associated Supernova 2003dh: The First Two Months. The Astrophysical Journal, 599(1), 394-407. doi:10.1086/379228
  More info

  We present extensive optical and infrared photometry of the afterglow of gamma-ray burst (GRB) 030329 and its associated supernova (SN) 2003dh over the first two months after detection (2003 March 30-May 29 UT). Optical spectroscopy from a variety of telescopes is shown and, when combined with the photometry, allows an unambiguous separation between the afterglow and SN contributions. The optical afterglow of the GRB is initially a power-law continuum but shows significant color variations during the first week that are unrelated to the presence of an SN. The early afterglow light curve also shows deviations from the typical power-law decay. An SN spectrum is first detectable ~7 days after the burst and dominates the light after ~11 days. The spectral evolution and the light curve are shown to closely resemble those of SN 1998bw, a peculiar Type Ic SN associated with GRB 980425, and the time of the SN explosion is close to the observed time of the GRB. It is now clear that at least some GRBs arise from core-collapse SNe.
• Finn, R., Zaritsky, D., McCarthy, D., Poggianti, B., Rudnick, G., Halliday, C., Milvang-Jensen, B., Pello, R., & Simard, L. (2003). H alpha-derived star formation rates for three z similar or equal to 0.75 EDisCS galaxy clusters. ASTROPHYSICAL JOURNAL, 630(1), 206-227.
• Knierman, K. A., Gallagher, S. C., Charlton, J. C., Hunsberger, S. D., Whitmore, B., Kundu, A., Hibbard, J. E., & Zaritsky, D. (2003). From globular clusters to tidal dwarfs: Structure formation in the tidal tails of merging galaxies. Astronomical Journal, 126(3 1773), 1227-1244.
  More info

  Abstract: Using V and I images obtained with the Wide Field Planetary Camera 2 (WFPC2) of the Hubble Space Telescope, we investigate compact stellar structures within tidal tails. Six regions of tidal debris in the four classic "Toomre sequence" mergers: NGC 4038/39 ("Antennae"), NGC 3256, NGC 3921, and NGC 7252 ("Atoms for Peace") have been studied in order to explore how the star formation depends on the local and global physical conditions. These mergers sample a range of stages in the evolutionary sequence and tails with and without embedded tidal dwarf galaxies. The six tails are found to contain a variety of stellar structures, with sizes ranging from those of globular clusters up to those of dwarf galaxies. From V and I WFPC2 images, we measure the luminosities and colors of the star clusters. NGC 3256 is found to have a large population of blue clusters (0.2 ≲ V-I ≲ 0.9), particularly in its western tail, similar to those found in the inner region of the merger. In contrast, NGC 4038/39 has no clusters in the observed region of the tail, only less luminous point sources likely to be individual stars. NGC 3921 and NGC 7252 have small populations of clusters along their tails. A significant cluster population is clearly associated with the prominent tidal dwarf candidates in the eastern and western tails of NGC 7252. The cluster-rich western tail of NGC 3256 is not distinguished from the others by its dynamical age or by its total H I mass. However, the mergers that have few clusters in the tail all have tidal dwarf galaxies, while NGC 3256 does not have prominent tidal dwarfs. We speculate that star formation in tidal tails may manifest itself either in small structures like clusters along the tail or in large structures such as dwarf galaxies, but not in both. Also, NGC 3256 has the highest star formation rate of the four mergers studied, which may contribute to the high number of star clusters in its tidal tails.
• Poggianti, B. M., Desai, V., Finn, R., Bamford, S., De Lucia, G., Varela, J., Aragon-Salamanca, A., Halliday, C., Noll, S., Saglia, R., Zaritsky, D., Best, P., Clowe, D., Milvang-Jensen, B., Jablonka, P., Pello, R., Rudnick, G., Simard, L., von der Linden, A., & White, S. (2003). The relation between star formation, morphology, and local density in high-redshift clusters and groups. ASTROPHYSICAL JOURNAL, 684(2), 888-904.
• Rottgering, H. J., Zaritsky, D., White, S. D., Simard, L., Schneider, P., Saglia, R. P., Rudnick, G., Rottgering, H., Poirier, S., Poggianti, B. M., Pello, R., Milvang-jensen, B., Mellier, Y., Lucia, G. D., Kauffmann, G., Jablonka, P., Halliday, C., Fort, B., Desai, V., , Dantel, M., et al. (2003). Studying high redshift galaxy clusters with the ESO distant cluster survey. The Messenger, 112, 19-24.
• Skillman, E., Kennicutt, R., Shields, G., & Zaritsky, D. (2003). Chemical abundances in Virgo spiral galaxies .2. Effects of cluster environment. ASTROPHYSICAL JOURNAL, 462(1), 147-162.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Gonzalez, A. H. (2003). Structural Properties of Brightest Cluster Galaxies. Astrophysics and Space Science, 285(1), 67-71. doi:10.1023/a:1024649423503
  More info

  We present the first modem systematic study of local brightest cluster galaxy (BCG) profiles that extends to radii beyond 200h -1 kpc. Measuring the surface brightness profiles of BCGs out to large radii is critical for understanding the processes driving their formation. The form of the profiles yields information about the current dynamical state, constrains the accretion history of these galaxies, and places limits on any radially symmetric component of intracluster light. The observational challenges associated with CCD photometry at low surface brightness levels have until now precluded such an analysis for a statistical sample of BCGs. Utilizing drift-scan data and new techniques that we have developed, we extend upon previous work by modelling the profiles for a sample of 31 clusters at z≃0.1 that span a wide range in mass and dynamical state. We find that the BCGs in our sample generally are best fit using two-component models consisting of inner and outer Sersic profiles. In this proceeding we present the preliminary results of our analysis and discuss implications for current models of BCG formation.
• Zaritsky, D., & Gonzalez, A. H. (2003). On the incidence of strong gravitational lensing by clusters in the Las Campanas distant cluster survey. Astrophysical Journal Letters, 584(2 I), 691-701.
  More info

  Abstract: The observed incidence of strongly lensing clusters exceeds the predictions of a ACDM model by about a factor of 10. We revisit the observational side of this discrepancy by measuring the incidence of strong lensing in a subsample of clusters drawn from the Las Campanas Distant Cluster Survey (LCDCS). Among clusters with 0.5 ≤ z ≤ 0.7, the redshift range in which we focus our search, we find two strongly lensed systems within an effective search area of 69 deg2. There is at least one other strongly lensed system in the LCDCS outside of this redshift range, where we are less complete. Over all redshifts, the ACDM model produces one large arc every 146 deg2. Assuming Poisson statistics, the probability of finding three or more strongly lensing clusters in 69 deg2 is 0.012. The lensing incidence within the LCDCS is in agreement with that derived from an X-ray-selected sample and what has been preliminarily presented from an independent optical cluster survey. The origin of the disagreement between theory and observations, which remains at least at the order-of-magnitude scale for the ACDM model, lies either in the concordance cosmological model, in the characteristics of the resulting cluster potentials, or in the adopted source population.
• Zaritsky, D., Vogel, S. N., Tully, R. B., Tonry, J. L., Shaya, E. J., Peebles, P. J., Nusser, A., & Borne, K. D. (2003). Space interferometry mission dynamical observations of galaxies (SIMDOG) key project. Astronomical Telescopes and Instrumentation, 4852(1), 120-130. doi:10.1117/12.460695
  More info

  The Space Interferometry Mission (SIM) spacecraft will be used to measure the proper motions for a sample of ~30 nearby galaxies. At this time there are no proper motion measurements of galaxies beyond the satellite systems of the Milky Way. With the capability of measuring absolute positions to 4 mas (microarcsecond) accuracy and a five-year baseline, SIM will be able to measure proper motions as small as 10 km/s over the Local Group and 40 km/s at 4 Mpc. The motion of each galaxy will be monitored by targeting 5-10 stars that are brighter than 20th magnitude. SIM measurements will lead to knowledge of the full 6-dimensional position and velocity vectors of each galaxy. In conjunction with gravitational flow modeling, improved total mass measurements of individual galaxies and the fractional contribution of dark matter to galaxies of the Local Group will be obtained. The project includes development of theoretical methods for orbital calculations.
• Bell, E. F., Gordon, K. D., Kennicutt Jr., R. C., & Zaritsky, D. (2002). The effects of dust in simple environments: Large magellanic cloud H II regions. Astrophysical Journal Letters, 565(2 I), 994-1010.
  More info

  Abstract: We investigate the effects of dust on Large Magellanic Cloud (LMc) H II region spectral energy distributions using arcminute-resolution far-ultraviolet (FUV), Hα, far-infrared (FIR), and radio images. Widely used indicators of the amount of light lost to dust (attenuation) at Hα and in the FUV correlate with each other, although often with substantial scatter. There are two interesting systematic discrepancies: First, Hα attenuations estimated from the Balmer decrement are lower than those estimated from the Hα-to-thermal radio luminosity ratio. Our data, at this stage, cannot unambiguously identify the source of this discrepancy. Second, the attenuation at 1500 Å and the UV spectral slope, β, correlate, although the slope and scatter are substantially different from the correlation first derived for star-bursting galaxies by Calzetti et al. Combining our result with those of Meurer et al. for ultraluminous infrared galaxies and Calzetti et al. for starbursting galaxies, we conclude that no single relation between β and 1500 Å attenuation is applicable to all star-forming systems.
• Bernard, J., Reach, W. T., Paradis, D., Meixner, M., Paladini, R., Kawamura, A., Onishi, T., Vijh, U., Gordon, K., Indebetouw, R., Hora, J. L., Whitney, B., Blum, R., Meade, M., Babler, B., Churchwell, E. B., Engelbracht, C. W., For, B., Misselt, K., , Leitherer, C., et al. (2002). Spitzer survey of the Large Magellanic Cloud, Surveying the Agents of a Galaxy's Evolution (sage). IV. Dust properties in the interstellar medium. ASTRONOMICAL JOURNAL, 136(3), 919-945.
• Gonzalez, A. H., Zaritsky, D., & Wechsler, R. H. (2002). The las campanas distant cluster survey correlation function. Astrophysical Journal Letters, 571(1 I), 129-135.
  More info

  Abstract: We present the first nonlocal (z > 0.2) measurement of the cluster-cluster spatial correlation length, using data from the Las Campanas Distant Cluster Survey (LCDCS). We measure the angular correlation function for velocity dispersion-limited subsamples of the catalog at estimated redshifts of 0.35 ≤ zest < 0.575 and derive spatial correlation lengths for these clusters via the cosmological Limber equation. The correlation lengths that we measure for clusters in the LCDCS are consistent both with local results for the APM cluster catalog and with theoretical expectations based upon the Virgo Consortium Hubble Volume simulations and the analytic predictions. Despite samples containing over 100 clusters, our ability to discriminate between cosmological models is limited because of statistical uncertainty.
• Gonzalez, A. H., Zaritsky, D., Simard, L., Clowe, D., & White, S. D. (2002). Tests of the Las Campanas Distant Cluster Survey from confirmation observations for the ESO Distant Cluster Survey. Astrophysical Journal Letters, 579(2 I), 577-586.
  More info

  Abstract: The ESO Distant Cluster Survey (EDisCS) is a photometric and spectroscopic study of the galaxy cluster population at two epochs, z ≃ 0.5 and z ≃ 0.8, drawn from the Las Campanas Distant Cluster Survey (LCDCS). We report results from the initial candidate-confirmation stage of the program and use these results to probe the properties of the LCDCS. Of the 30 candidates targeted, we find statistically significant overdensities of red galaxies near 28. Of the 10 additional candidates serendipitously observed within the fields of the targeted 30, we detect red galaxy overdensities near six. We test the robustness of the published LCDCS estimated redshifts to misidentification of the brightest cluster galaxy (BCG) in the survey data and measure the spatial alignment of the published cluster coordinates, the peak red galaxy overdensity, and the BCG. We conclude that for LCDCS clusters out to z ∼ 0.8, (1) the LCDCS coordinates agree with the centroid of the red galaxy overdensity to within 25″ (∼ 150 h-1 kpc) for 34 out of 37 candidates with 3 σ galaxy overdensities, (2) BCGs are typically coincident with the centroid of the red galaxy population to within a projected separation of 200 h-1 kpc (32 out of 34 confirmed candidates), (3) the red galaxy population is strongly concentrated, and (4) the misidentification of the BCG in the LCDCS causes a redshift error greater than 0.1 in 15%-20% of the LCDCS candidates. These findings together help explain the success of the surface brightness fluctuations detection method.
• Nelson, A. E., Gonzalez, A. H., Zaritsky, D., & Dalcanton, J. J. (2002). Revisiting brightest cluster galaxy evolution with the Las Campanas distant cluster survey. Astrophysical Journal Letters, 566(1 I), 103-122.
  More info

  Abstract: We investigate the influence of environment on brightest cluster galaxy (BCG) evolution using a sample of 63 clusters at 0.3 ≤ z ≤ 0.9 drawn primarily from the Las Campanas Distant Cluster Survey and follow-up V, I, and K′ photometry. The luminosity evolution of the entire BCG sample is not adequately described by a single evolutionary model. Using the integrated light from the cluster detection as a proxy for cluster Lx and the suggestion by Burke, Collins, & Mann, we set Lx = 2 × 1044 ergs s-1 to be the division between high- and low-luminosity clusters. At high redshift (z > 0.6) BCGs from low-L x clusters are fainter, on average, than those from high-L x clusters and are best modeled as having constant luminosity with redshift. The BCGs from high-Lx clusters are best modeled as having a stellar population that formed at large redshift (zform > 5) and is passively evolving. However, for the entire BCG population, the observed V - I and I - K′ colors are well described by a single evolutionary model in which the stellar populations have zform > 5 and subsequently passively evolve. We conclude that accretion is proportionally more significant for BCGs in lower mass clusters at these redshifts (a factor of 2-4 increase in mass since z ∼ l for the low-Lx systems; Aragon-Salamanca and coworkers) and that the accreted matter is in the form of systems with evolved stellar populations.
• Nelson, A. E., Simard, L., Zaritsky, D., Dalcanton, J. J., & Gonzalez, A. H. (2002). Constraints on the size evolution of brightest cluster galaxies. Astrophysical Journal Letters, 567(1 I), 144-154.
  More info

  Abstract: We measure the luminosity profiles of 16 brightest cluster galaxies (BCGs) at 0.4 < z < 0.8 using high-resolution F160W NICMOS and F814W WFPC2 Hubble Space Telescope imaging. The heterogeneous sample is drawn from a variety of surveys: seven from clusters in the Einstein Medium Sensitivity Survey, five from the Las Campanas Distant Cluster Survey and its Northern Hemisphere precursor, and the remaining four from traditional optical surveys. We find that the surface brightness profiles of all but three of these BCGs are well described by a standard de Vaucouleurs (r1/4) profile out to at least ∼ 2re and that the biweight-estimated NICMOS effective radius of our high-redshift BCGs (re = 8.3 ± 1.4 kpc for H0 = 80 km s-1 Mpc-1, Ωm = 0.2, ΩΛ = 0.0) is ∼ 2 times smaller than that measured for a local BCG sample. If high-redshift BCGs are in dynamical equilibrium and satisfy the same scaling relations as low-redshift ones, this change in size would correspond to a mass growth of a factor of 2 since z ∼ 0.5. However, the biweight-estimated WFPC2 effective radius of our sample is 18 ± 5.1 kpc, which is fully consistent with the local sample. While we can rule out mass accretion rates higher than a factor of 2 in our sample, the discrepancy between our NICMOS and WFPC2 results, which after various tests we describe appears to be physical, does not yet allow us to place strong constraints on accretion rates below that level.
• Shaya, E., Tully, R. B., Peebles, P. J., Tonry, J. L., Borne, K., Vogel, S. N., Nusser, A., & Zaritsky, D. (2002). Space Interferometry Mission - Dynamical Observations of Galaxies (SIMDOG) key project. Proceedings of SPIE - The International Society for Optical Engineering, 4852(1), 120-130.
  More info

  Abstract: The Space Interferometry Mission (SIM) spacecraft will be used to measure the proper motions for a sample of ∼30 nearby galaxies. At this time there are no proper motion measurements of galaxies beyond the satellite systems of the Milky Way. With the capability of measuring absolute positions to 4 μas (microarcsecond) accuracy and a five-year baseline, SIM will be able to measure proper motions as small as 10 km/s over the Local Group and 40 km/s at 4 Mpc. The motion of each galaxy will be monitored by targeting 5-10 stars that are brighter than 20th magnitude. SIM measurements will lead to knowledge of the full 6-dimensional position and velocity of each galaxy. In conjunction with gravitational flow modeling, improved total mass measurements of individual galaxies and the fractional contribution of dark matter to galaxies of the Local Group will be obtained. The project includes development of theoretical methods for orbital calculations.
• Wittman, D., Tyson, J. A., Dell'Antonio, I., Becker, A. C., Margoniner, V. E., Cohen, J., Norman, D., Loomba, D., Squires, G., Wilson, G., Stubbs, C., Hennawi, J., Spergel, D., Boeshaar, P., Clocchiatt, A., Hamuy, M., Bernstein, G., Gonzalez, A., Guhathakurta, P., , Hu, W., et al. (2002). The deep lens survey. Proceedings of SPIE - The International Society for Optical Engineering, 4836, 73-82.
  More info

  Abstract: The Deep Lens Survey (DLS) is a deep BV Rz′ imaging survey of seven 2° × 2° degree fields, with all data to be made public. The primary scientific driver is weak gravitational lensing, but the survey is also designed to enable a wide array of other astrophysical investigations. A unique feature of this survey is the search for transient phenomena. We subtract multiple exposures of a field, detect differences, classify, and release transients on the Web within about an hour of observation. Here we summarize the scientific goals of the DLS, field and filter selection, observing techniques and current status, data reduction, data products and release, and transient detections. Finally, we discuss some lessons which might apply to future large surveys such as LSST.
• Zaritsky, D., Harris, J., Thompson, I. B., Grebel, E. K., & Massey, P. (2002). The magellanic clouds photomtric survey: The small magellanic cloud stellar catalog and extinction map. Astronomical Journal, 123(2 1754), 855-872.
  More info

  Abstract: We present our catalog of U, B, V, and I stellar photometry of the central 18 deg2 area of the Small Magellanic Cloud. We combine our data with the Two Micron All Sky Survey and Deep Near-Infrared Southern Sky Survey (DENIS) catalogs to provide, when available, U through Ks data for stars. Internal and external astrometric and photometric tests using existing optical photometry (U, B, and V from Massey's bright star catalog; B, V, and 7 from the microlensing database of OGLE; and 7 from the near-infrared sky survey DENIS) are used to determine the observational uncertainties and identify systematic errors. We fit stellar atmosphere models to the optical data to check the consistency of the photometry for individual stars across the passbands and to estimate the line-of-sight extinction. Finally, we use the estimated line-of-sight extinctions to produce an extinction map across the Small Magellanic Cloud, and we investigate the nature of extinction as a function of stellar population.
• van Velzen, S., Farrar, G. R., Gezari, S., Morrell, N., Zaritsky, D., Oestman, L., Smith, M., Gelfand, J., & Drake, A. J. (2002). OPTICAL DISCOVERY OF PROBABLE STELLAR TIDAL DISRUPTION FLARES. ASTROPHYSICAL JOURNAL, 741(2).
• Chang, T. C., van Gorkom, J. H., Zabludoff, A. I., Zaritsky, D., & Mihos, J. C. (2001). Search for HI in E+A galaxies. ASTRONOMICAL JOURNAL, 121(4), 1965-1973.
• Desai, V., Dalcanton, J. J., Aragon-Salamanca, A., Jablonka, P., Poggianti, B., Gogarten, S. M., Simard, L., Milvang-Jensen, B., Rudnick, G., Zaritsky, D., Clowe, D., Halliday, C., Pello, R., Saglia, R., & White, S. (2001). The morphological content of 10 EDisCS clusters at 0.5 < z < 0.8. ASTROPHYSICAL JOURNAL, 660(2), 1151-1164.
• Gallagher, S. C., Charlton, J. C., Hunsberger, S. D., Zaritsky, D., & Whitmore, B. C. (2001). Hubble Space Telescope images of Stephan's Quintet: Star cluster formation in a compact group environment. Astronomical Journal, 122(1), 163-181.
  More info

  Abstract: Analysis of Hubble Space Telescope Wide Field Planetary Camera 2 images of Stephan's Quintet, Hickson Compact Group 92, yielded 115 candidate star clusters (with V-I < 1.5). Unlike in merger remnants, the cluster candidates in Stephan's Quintet are not clustered in the inner regions of the galaxies; they are spread over the debris and surrounding area. Specifically, these sources are located in the long sweeping tail and spiral arms of NGC 7319, in the tidal debris of NGC 7318B/A, and in the intragroup starburst region north of these galaxies. Analysis of the colors of the clusters indicate several distinct epochs of star formation that appear to trace the complex history of dynamical interactions in this compact group.
• Gonzalez, A. H., Zaritsky, D., Dalcanton, J. J., & Nelson, A. (2001). The Las Campanas Distant Cluster Survey: The catalog. Astrophysical Journal, Supplement Series, 137(1), 117-138.
  More info

  Abstract: We present an optically selected catalog of 1073 galaxy cluster and group candidates at 0.3 ≲ z ≲ 1. These candidates are drawn from the Las Campanas Distant Clusters Survey (LCDCS), a drift-scan imaging survey of a 130 square degree strip of the southern sky. To construct this catalog we utilize a novel detection process in which clusters are detected as positive surface brightness fluctuations in the background sky. This approach permits us to find clusters with significantly shallower data than other matched-filter methods that are based upon number counts of resolved galaxies. Selection criteria for the survey are fully automated so that this sample constitutes a well-defined, homogeneous sample that can be used to address issues of cluster evolution and cosmology. Estimated redshifts are derived for the entire sample, and an observed correlation between surface brightness and velocity dispersion, σ, is used to estimate the limiting velocity dispersion of the survey as a function of redshift. We find a net surface density of 15.5 candidates per square degree at zest ≥ 0.3, with a false-detection rate of ∼30%. At z ∼ 0.3 we probe down to the level of poor groups while by z ∼ 0.8 we detect only the most massive systems (σ ≳ 1000 km s-1). We also present a supplemental catalog of 112 candidates that fail one or more of the automated selection criteria, but appear from visual inspection to be bona fide clusters.
• Harris, J., & Zaritsky, D. (2001). A method for determining the star formation history of a mixed stellar population. Astrophysical Journal, Supplement Series, 136(1), 25-40.
  More info

  Abstract: We present a method to determine the star formation history of a mixed stellar population from its photometry. We perform a χ2 minimization between the observed photometric distribution and a model photometric distribution, based on theoretical isochrones. The initial mass function, distance modulus, interstellar reddening, binary fraction, and photometric errors are incorporated into the model, making it directly comparable to the data. The model is a linear combination of individual synthetic color-magnitude diagrams (CMDs), each of which represents the predicted photometric distribution of a stellar population of a given age and metallicity. While the method is similar to existing synthetic CMD algorithms, we describe several key improvements in our implementation. In particular, we focus on the derivation of accurate error estimates on the star formation history to enable comparisons between such histories, either from different objects or from different regions of a single object. We present extensive tests of the algorithm, using both simulated and actual photometric data. From a preliminary application of the algorithm to a subregion of the Large Magellanic Cloud (LMC), we find that the that the lull in star formation observed among the LMC's cluster population between 3 and 8 Gyr ago is also present in the field population. The method was designed with flexibility and generality in mind, and we make the code available for use by the astronomical community.
• Nelson, A. E., Gonzalez, A. H., Zaritsky, D., & Dalcanton, J. J. (2001). Cluster galaxy evolution from a new sample of galaxy clusters at 0.3 < z < 0.9. Astrophysical Journal Letters, 563(2 PART 1), 629-652.
  More info

  Abstract: We analyze photometry and spectroscopy of a sample of 63 clusters at 0.3 ≤ z ≤ 0.9 drawn from the Las Campanas Distant Cluster Survey to empirically constrain models of cluster galaxy evolution. Specifically, (1) by combining I-band photometry of 44 of our clusters with that of 19 clusters from the literature, we parameterize the redshift dependence of M*I in the observed frame as M*I = (-21.74 ± 0.12) - (0.88 + 0.24)z - 5 log h (rms deviation = 0.34) for 0.3 ≤ z ≤ 0.9 (Ω0 = 02, ΩΛ = 0); (2) by combining 30 of our clusters and 14 clusters from the literature with V and I data, we parameterize the redshift dependence of the V-I color of the E/S0 red sequence in the observed frames as V-I = (-0.24 ± 0.28) + (7.42 ± 1.03)z - (4.61 ± 0.91)z2 (rms deviation = 0.16) for 0.3 ≤ z ≤ 0.9; and (3) by combining 13 of our clusters with 15 clusters from the literature with I and K′ data, we parameterize the redshift dependence of the I-K′ color of the E/S0 red sequence in the observed frames as I-K′ = (0.66 ± 0.65) + (9.50 ± 3.72)z - (14.72 ± 7.01)z2 + (8.72 ± 4.29)z3 (rms deviation = 0.18) for 0.3 ≤ z ≤ 0.9. Using the peak surface brightness of the cluster detection, Σ, as a proxy for cluster mass, we find no correlation between Σ and M*I or the location of the red envelope in V-I. We suggest that these observations can be explained with a model in which luminous early-type galaxies (or more precisely, the progenitors of current-day luminous early-type galaxies) form the bulk of their stellar populations at high redshifts (≳5) and in which many of these galaxies, if not all, accrete mass either in the form of evolved stellar populations or gas that causes only a short-term episode of star formation at lower redshifts (1.5 < z < 2). Our data are too crude to reach conclusions regarding the evolutionary state of any particular cluster or to investigate whether the morphological evolution of galaxies matches the simple scenario that we discuss, but the statistical nature of this study suggests that the observed evolutionary trends are universal in massive clusters.
• Norton, S. A., Gebhardt, K., Zabludoff, A. I., & Zaritsky, D. (2001). The spatial distribution and kinematics of stellar populations in E+A galaxies. ASTROPHYSICAL JOURNAL, 557(1), 150-164.
• Parker, J. W., Zaritsky, D., Stecher, T. P., Harris, J., & Massey, P. (2001). Ultraviolet and optical observations of ob associations and field stars in the southwest region of the Large Magellanic Cloud. Astronomical Journal, 121(2), 891-904.
  More info

  Abstract: Using ultraviolet photometry from the Ultraviolet Imaging Telescope (UIT) combined with photometry and spectroscopy from three ground-based optical data sets we have analyzed the stellar content of OB associations and field areas in and around the regions N79, N81, N83, and N94 in the Large Magellanic Cloud. In particular, we compare data for the OB association Lucke-Hodge 2 (LH 2) to determine how strongly the initial mass function (IMF) may depend on different photometric reductions and calibrations. Although the data sets exhibit median photometric differences of up to 30%, the resulting uncorrected IMFs are reasonably similar, typically Γ ∼ -1.6 in the 5-60 M⊙ mass range. However, when we correct for the background contribution of field stars, the calculated IMF flattens to Γ = -1.3 ± 0.2 (similar to the Salpeter IMF slope). This change underlines the importance of correcting for field star contamination in determinations of the IMF of star formation regions. It is possible that even in the case of an universal IMF, the variability of the density of background stars could be the dominant factor creating the differences between calculated IMFs for OB associations. We have also combined the UIT data with the most extensive of these ground-based optical data sets - the Magellanic Cloud Photometric Survey - to study the distribution of the candidate O-type stars in the field. We find a significant fraction, roughly half, of the candidate O-type stars are found in field regions, far from any obvious OB associations (in accord with the 1982 suggestions of Garmany, Conti, & Chiosi for O-type stars in the solar neighborhood). These stars are greater than 2′ (30 pc) from the boundaries of existing OB associations in the region, which is a distance greater than most O-type stars with typical dispersion velocities will travel in their lifetimes. The origin of these massive field stars (either as runaways, members of low-density star-forming regions, or examples of isolated massive star formation) will have to be determined by further observations and analysis.
• Zaritsky, D., & Lin, D. (2001). Evidence for an intervening stellar population toward the Large Magellanic Cloud. ASTRONOMICAL JOURNAL, 114(6), 2545-&.
• Zaritsky, D., Smith, R., Frenk, C., & White, S. (2001). More satellites of spiral galaxies. ASTROPHYSICAL JOURNAL, 478(1), 39-48.
• Zaritsky, D., Zabludoff, A. I., Christlein, D., & Balogh, M. L. (2001). The environmental dependence of the infrared luminosity and stellar mass functions. The Astrophysical Journal, 557(1), 117-125. doi:10.1086/321670
  More info

  We investigate the dependence of the galaxy infrared luminosity function (LF) and the associated stellar mass function (SMF) on environment and spectral type using photometry from the Two Micron All Sky Survey and redshifts from the Las Campanas Redshift Survey for galaxies brighter than MJ < -19 + 5 log h. In the field environment, the LFs of galaxies with emission lines have much steeper faint-end slopes (?J = -1.39) than those of galaxies without emission lines (?J = -0.59). In the cluster environment, however, even the non-emission-line galaxies have a steep faint-end LF (?J = -1.22). There is also a significant (95%) difference between the overall cluster and field LFs, ??J = -0.34 and ?M*J = -0.54. All these variations are more pronounced in the SMFs, which we compute by relating the strength of the 4000 ? break in the optical spectra to a stellar mass-to-light ratio.
• Clowe, D., Bradac, M., Gonzalez, A. H., Markevitch, M., Randall, S. W., Jones, C., & Zaritsky, D. (2000). A direct empirical proof of the existence of dark matter. ASTROPHYSICAL JOURNAL, 648(2), L109-L113.
• Sakai, S., Zaritsky, D., & Kennicutt Jr., R. C. (2000). The tip of the red giant branch distance to the Large Magellanic Cloud. Astronomical Journal, 119(3), 1197-1204.
  More info

  Abstract: We present the I-band luminosity function of the red giant branch stars in the Large Magellanic Cloud (LMC) using the data from the Magellanic Clouds Photometric Survey (MCPS). By selecting stars in uncrowded, low-extinction regions, we observe a discontinuity in the luminosity function at I0 = 14.54 mag. Identifying this feature with the tip of the red giant branch (TRGB) and adopting an absolute TRGB magnitude of -4.05 ± 0.04 based on the calibration of Lee, Freedman, & Madore, we obtain a distance modulus of 18.59 ± 0.09 (random) ± 0.16 (systematic) mag. If the theoretical TRGB calibration provided by Cassisi & Salaris is adopted instead, the derived distance would be 4% greater. The LMC distance modulus reported here, 18.59 ± 0.09, is larger by 0.09 mag (1 σ) than the value that is most commonly used in the extragalactic distance scale calibrated by the period-luminosity relation of the Cepheid variable stars. Our TRGB distance modulus agrees with several RR Lyrae distances to the LMC based on Hipparcos parallaxes. Finally, we note that, by using the same MCPS data, we obtain a distance modulus of 18.29 ± 0.03 mag using the red clump method, which yields a distance shorter by 0.3 mag compared with the TRGB estimate.
• Sakai, S., Zaritsky, D., & Kennicutt, R. C. (2000). The tip of the red giant branch distance to the Large Magellanic Cloud. ASTRONOMICAL JOURNAL, 119(3), 1197-1204.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., Gonzalez, A. H., & Dalcanton, J. J. (2000). Measuring the diffuse optical light in Abell 1651. The Astrophysical Journal, 536(2), 561-570. doi:10.1086/308985
  More info

  Using drift-scan data, a new approach to determining surface brightness profiles, and techniques for detecting low surface brightness signals, we fit the light profile of the brightest cluster galaxy (BCG) in the rich cluster Abell 1651 out to 670 h-1 kpc. This radius is a significant fraction of the virial radius of the cluster (2 h-1 Mpc), indicating that the sizes of the BCG and the cluster are comparable. We find that the profile is consistent with a de Vaucouleurs profile over the radial range probed. We also find that the integrated light profile of the BCG in Abell 1651 contributes 36% of the total cluster light within 500 h-1 kpc. Including all luminous components, we obtain M/LI ~ 160 h for the cluster, which would be overestimated by ~20% without the BCG halo. Furthermore, the relatively red color of the BCG at large radii suggests that recent disruption and tidal stripping of spirals and dwarf ellipticals do not contribute significantly to the halo luminosity. The color and the form of the profile are consistent with a scenario in which the BCG forms from filamentary collapse during the epoch of cluster formation, with relatively little evolution in the past 5 Gyr. We remove the BCG and other detected galaxies from the image and construct a two-dimensional surface brightness map of the cluster core. Several knots of excess emission are found, but the total diffuse component is constrained to contribute less than 5% of the cluster light.
• Zaritsky, D., Harris, J., Grebel, E. K., & Thompson, I. B. (2000). The morphologies of the Small Magellanic Cloud. ASTROPHYSICAL JOURNAL, 534(1), L53-L56.
• Zaritsky, D., Harris, J., Grebel, E. K., & Thompson, I. B. (2000). The morphologies of the small magellanic cloud. Astrophysical Journal Letters, 534(1 PART 2), L53-L56.
  More info

  Abstract: We compare the distribution of stars of different spectral types, and hence mean age, within the central SMC and find that the asymmetric structures are almost exclusively composed of young main-sequence stars. Because of the relative lack of older stars in these features and the extremely regular distribution of red giant and clump stars in the SMC central body, we conclude that tides alone are not responsible for the irregular appearance of the central SMC. The dominant physical mechanism in determining the current-day appearance of the SMC must be star formation triggered by a hydrodynamic interaction between gaseous components. These results extend the results of population studies (see Gardiner & Hatzidimitriou) inward in radius and also confirm the suggestion of the spheroidal nature of the central SMC based on kinematic arguments (Dopita et al.; Hardy, Suntzeff, & Azzopardi). Finally, we find no evidence in the underlying older stellar population for a "bar" or "outer arm," again supporting our classification of the central SMC as a spheroidal body with highly irregular recent star formation.
• Zaritsky, D., Hunsberger, S. D., & Charlton, J. C. (2000). The Luminosity Function of Galaxies in Compact Groups. International Astronomical Union Colloquium, 174, 81-85. doi:10.1017/s0252921100054798
  More info

  From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts to determine a luminosity function extending to MR = -14.0+5 log h75, approximately 2 mag deeper than previous compact group luminosity functions. We find that a single Schechter function is a poor fit (χ$2{ν}$ -->$t SUPgt 2t/SUPgt t SUBgt {ν}t/SUBgt $ -->$t Igt tt/Igt SUPgt 2t/SUPgt t SUBgt {ν}t/SUBgt $ -->>4) to the data, so we fit a composite function consisting of separate Schechter functions for the bright and faint galaxies. The bright end is best fit with M* = -21.6 and α = -0.52, and the faint end with M* = -16.1 and α = -1.17. The decreasing bright-end slope implies a deficit of intermediate-luminosity galaxies in our sample of HCGs, and the faint-end slope is slightly steeper than that reported for earlier HCG luminosity functions. Furthermore, luminosity functions of subsets of our sample reveal more substantial dwarf populations for groups with X-ray halos, groups with tidal dwarf candidates, and groups with a dominant elliptical or lenticular galaxy. Collectively, these results support the hypothesis that within compact groups, the initial dwarf galaxy population is replenished by subsequent generations formed in the tidal debris of giant galaxy interactions.
• Harris, J., & Zaritsky, D. (1999). On the spatial distribution of stellar populations in the large magellanic cloud. ASTRONOMICAL JOURNAL, 117(6), 2831-2840.
• Harris, J., & Zaritsky, D. (1999). On the spatial distribution of stellar populations in the large magellanic cloud. Astronomical Journal, 117(6), 2831-2840.
  More info

  Abstract: We measure the angular correlation function of stars in a region of the Large Magellanic Cloud (LMC) that spans 2°.0 × 1°.5. We find that the correlation functions of stellar populations are represented well by exponential functions of the angular separation for separations between 2′ and 40′ (corresponding to ∼30 and 550 pc for an LMC distance of 50 kpc). The inner boundary is set by the presence of distinct, highly correlated structures, which are the more familiar stellar clusters, and the outer boundary is set by the observed region's size and the presence of two principal centers of star formation within the region. We also find that the normalization and scale length of the correlation function changes systematically with the mean age of the stellar population. The existence of positive correlation at large separations (∼300 pc), even in the youngest population, argues for large-scale hierarchical structure in current star formation. The evolution of the angular correlation toward lower normalizations and longer scale lengths with stellar age argues for the dispersion of stars with time. We show that a simple, stochastic, self-propagating star formation model is qualitatively consistent with this behavior of the correlation function.
• Kobulnicky, H. A., & Zaritsky, D. (1999). Chemical properties of star-forming emission-line galaxies at z = 0.1-0.5. Astrophysical Journal Letters, 511(1 PART 1), 118-135.
  More info

  Abstract: We measure the H II-region oxygen and nitrogen abundances for 14 star-forming emission-line galaxies (ELGs) at intermediate redshifts (0.11 < z < 0.5) using optical spectra obtained with the Keck II telescope and low-resolution imaging multiobject spectrograph. The target galaxies exhibit a range of metallicities from slightly metal poor, as in the LMC [12 + log (O/H) ≃ 8.4], to supersolar [12 + log (O/H) ≃ 9.05] where the solar value is 12 + log (O/H) ≃ 8.89. Oxygen abundances of the sample correlate strongly with rest-frame blue luminosities. The metallicity-luminosity relation based on these 14 objects is formally indistinguishable from the one obeyed by galaxies in the local universe, although there is marginal evidence (1.1 σ) that the sample is slightly more metal-deficient than local galaxies of the same luminosity. The observed galaxies exhibit smaller emission line widths than local galaxies of similar metallicity, but proper corrections for inclination angle and other systematic effects are unknown. For eight of the 14 objects we measure nitrogen-to-oxygen (N/O) ratios. Seven of the eight systems show evidence for secondary nitrogen production, with log (N/O) > -1.4, similar to local spiral galaxies. These chemical properties are inconsistent with unevolved objects undergoing a first burst of star formation. Comparison with local galaxies showing similar chemical properties suggests that these intermediate-z objects contain substantial old stellar populations that were responsible for the bulk of the heavy elements presently seen in the ionized gas. Four of the 14 galaxies exhibit small half-light radii and narrow emission-line profiles (compact narrow emission-line galaxies [CNELGs]; Koo et al. 1995) consistent with small dynamical masses despite their large optical luminosities and high levels of chemical enrichment. We find that the four CNELGs are indistinguishable from the 10 other emission-line galaxies (ELGs) in the sample on the basis of their metallicity and luminosity alone. Because of their morphological similarity to H II and spheroidal galaxies, CNELGs have been proposed as the starburst progenitors of today's spheroidal galaxies. Our assessment of the stellar chemical abundances in nearby spheroidal galaxies reveals that the majority of the CNELGs are presently ∼ 4 mag brighter and ∼ 0.5 dex more metal rich than the bulk of the stars in well-known metal-poor dwarf spheroidal galaxies such as NGC 205 and NGC 185. Two of the four CNELGs exhibit oxygen abundances higher than the planetary nebula oxygen abundances in NGC 205, making an evolution between these two CNELGs and metal-poor dwarf spheroidal galaxies highly improbable. However, the data are consistent with the hypothesis that more luminous and metal-rich spheroidal galaxies like NGC 3605 may become the evolutionary endpoints of some CNELGs after 1-3 mag of fading. We suggest that the z = 0.1-0.4 ELGs, and perhaps some of the CNELGs, are the precursors to today's spiral galaxies during an episode of vigorous bulge star formation ∼ 5 Gyr ago.
• Thompson, I. M., Zaritsky, D., Thompson, I. B., Harris, J., & Grebel, E. K. (1999). Reconstructing the Star Formation History of the Magellanic Clouds. Symposium - International Astronomical Union, 192, 72-78. doi:10.1017/s0074180900203926
  More info

  We are developing an algorithm to determine the star formation history (SFH) of a mixed stellar population. We will apply the algorithm to hundreds of regions in our Magellanic Clouds Photometric Survey data and reconstruct the spatially resolved star formation history of the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). In this paper, we demonstrate the algorithm on a typical region in the LMC, focussing on the obstacles and challenges facing us in attempting to reliably extract the SFH from photometric data.
• Thompson, I. M., Zaritsky, D., Thompson, I. B., Harris, J., & Grebel, E. K. (1999). Young Magellanic Cloud Clusters (< 1 Gyr): Census Properties, Star Formation History. Symposium - International Astronomical Union, 190, 405-409. doi:10.1017/s0074180900118418
  More info

  We report preliminary results from an automated cluster survey of the Magellanic Clouds aimed at improving the cluster census and at deriving cluster properties from their resolved stellar content. The survey is tripling the number of known clusters. The cluster age distribution shows similar peaks at 100–200 Myr in LMC and SMC, coincident with the closest encounter of the Clouds and perigalacticon.
• ZARITSKY, D. (1999). PRELIMINARY EVIDENCE FOR DUST IN GALACTIC HALOS. ASTRONOMICAL JOURNAL, 108(5), 1619-1626.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., Mihos, C., Gorkom, J. H., & Chang, T. (1999). A search for H I in spectroscopically selected E+A galaxies.. Bulletin of the American Astronomical Society, 31(4).
• Zaritsky, D. (1999). Dust and stellar populations in the Large Magellanic Cloud. Astronomical Journal, 118(6), 2824-2838.
  More info

  Abstract: We present an analysis of line-of-sight extinction measurements obtained using data from the Magellanic Clouds Photometric Survey (Zaritsky, Harris, & Thompson), which provides four-filter photometry for millions of stars in the Large Magellanic Cloud. We find that visual extinctions are typically larger by several tenths of a magnitude for stars with effective temperatures greater than 12,000 K than for stars with effective temperatures between 5500 and 6500 K. Several repercussions of this population-dependent extinction are discussed. In particular, LMC distance measurements that utilize old stellar populations, but use extinctions derived from OB stars, may be biased low. As a specific example, we show that the LMC distance modulus derived from field red clump stars is revised upward relative to published measurements by ∼0.2 mag if one uses the extinction measured for a matched stellar population. Conversely, measurements that utilize the youngest stars are subject to greater, and more variable, extinction leading preferentially to results that may be biased high. Population-dependent extinction affects the interpretation of color-magnitude diagrams and results in an effective absorption law that is steeper than that intrinsic to the dust for unresolved stellar systems. We further explore the relation between the stellar populations and dust by comparing our extinction map to the 100 μm image of the region and identifying potential heating sources of the dust. We find that although regions of high 100 μm flux are associated with young stars, young stars are not necessarily associated with regions of high 100 μm flux and that ∼50% of the 100 μm flux is emitted beyond the immediate regions of high OB stellar density. We conclude that 100 μm flux should be used with caution as a star formation tracer, particularly for studies of star formation within galaxies. Finally, we reproduce the observed extinction variation between the hot and cold stellar populations with a simple model of the distribution of the stars and dust in which the scale height of the cooler stars is much greater than that of the dust (which is twice that of the OB stars; Harris, Zaritsky, & Thompson).
• Zaritsky, D., & Gonzalez, A. H. (1999). Some implications of the anisotropic distribution of satellite galaxies. Publications of the Astronomical Society of the Pacific, 111(766), 1508-1514.
  More info

  Abstract: We examine a possible connection between the anisotropic distribution of satellite galaxies around giant spiral galaxies and the evolution of satellite systems. The observed polar anisotropy either is imprinted by initial conditions or develops from an initially symmetric distribution. We attempt to discriminate between these two possibilities by exploring the implications of the latter one. From the observed distribution of satellite galaxies relative to the primary galaxy's disk, we derive constraints on the orbital inclinations of the current satellite population. Using this derived inclination limit and assuming that the initial population had no preferred orbital inclination, we estimate the size of the hypothesized original population. We find that our best-fit models imply a population of destroyed (or inhibited) satellites whose combined luminosity (assuming the same M/L as for the observed satellites) is between 18% and 103% of the current disk luminosity.
• Zaritsky, D., & Kobulnicky, H. A. (1999). CHEMICAL PROPERTIES OF STAR-FORMING EMISSION-LINE GALAXIES AT z \ 0.1¨0.5. The Astrophysical Journal, 511(1), 118-135. doi:10.1086/306673
  More info

  We measure the H II-region oxygen and nitrogen abundances for 14 star-forming emission-line galaxies (ELGs) at intermediate redshifts (0.11 -1.4, similar to local spiral galaxies. These chemical properties are inconsistent with unevolved objects undergoing a first burst of star formation. Comparison with local galaxies showing similar chemical properties suggests that these intermediate-z objects contain substantial old stellar populations that were responsible for the bulk of the heavy elements presently seen in the ionized gas. Four of the 14 galaxies exhibit small half-light radii and narrow emission-line profiles (compact narrow emission-line galaxies [CNELGs]; Koo et al. 1995) consistent with small dynamical masses despite their large optical luminosities and high levels of chemical enrichment. We find that the four CNELGs are indistinguishable from the 10 other emission-line galaxies (ELGs) in the sample on the basis of their metallicity and luminosity alone. Because of their morphological similarity to H II and spheroidal galaxies, CNELGs have been proposed as the starburst progenitors of today's spheroidal galaxies. Our assessment of the stellar chemical abundances in nearby spheroidal galaxies reveals that the majority of the CNELGs are presently ~4 mag brighter and ~0.5 dex more metal rich than the bulk of the stars in well-known metal-poor dwarf spheroidal galaxies such as NGC 205 and NGC 185. Two of the four CNELGs exhibit oxygen abundances higher than the planetary nebula oxygen abundances in NGC 205, making an evolution between these two CNELGs and metal-poor dwarf spheroidal galaxies highly improbable. However, the data are consistent with the hypothesis that more luminous and metal-rich spheroidal galaxies like NGC 3605 may become the evolutionary endpoints of some CNELGs after 1-3 mag of fading. We suggest that the z=0.1-0.4 ELGs, and perhaps some of the CNELGs, are the precursors to today's spiral galaxies during an episode of vigorous bulge star formation ~5 Gyr ago.
• Zaritsky, D., & Rix, H. (1999). Lopsided Galaxies and the Satellite Accretion Rate. Symposium - International Astronomical Union, 186, 117-124. doi:10.1017/s0074180900112355
  More info

  Although current observations and theoretical models indicate that galaxy mergers and interactions are catalysts in the process of galaxy evolution, we have only a limited quantitative understanding of some basic aspects of the process. For example, the rate at which galaxies merge is poorly constrained. We can simplify the problem by considering only disk galaxies, which because of the fragility of their disks (cf. Toth and Ostriker 1992) have presumably not suffered a major merger. Even so, these galaxies have almost certainly experienced the infall of small companion galaxies at some time. The Milky Way is currently experiencing the accretion of the Sagittarius dwarf (Ibata, Gilmore, & Irwin 1994) and will eventually accrete the Magellanic Clouds (Tremaine 1976). To understand how galaxies evolve, we need to have quantitative knowledge of the accretion rate as a function of mass for all types of galaxies. Here we consider only the accretion of companion galaxies (∼ 10% by mass) onto large spiral galaxies.
• Zaritsky, D., Harris, J., Thompson, I., Grebel, E., & Massey, P. (1999). The Magellanic Clouds photometric survey: The Small Magellanic Cloud stellar catalog and extinction map. ASTRONOMICAL JOURNAL, 123(2), 855-872.
• Zaritsky, D., Shectman, S. A., Thompson, I., Harris, J., & Lin, D. N. (1999). Constraints on intervening stellar populations toward the Large Magellanic Cloud. Astronomical Journal, 117(5), 2268-2285.
  More info

  Abstract: The suggestion by Zaritsky & Lin (ZL) that a vertical extension of the red clump feature (the VRC) in color-magnitude diagrams (CMDs) of the Large Magellanic Cloud is consistent with a significant population of foreground stars to the LMC that could account for the observed microlensing optical depth has been challenged by various investigators. We respond by (1) examining each of the challenges presented, to determine whether any or all of those arguments invalidate the claims made by ZL, and (2) presenting new photometric and spectroscopic data obtained in an attempt to resolve this issue. We systematically discuss why the objections raised so far do not unequivocally refute ZL's claim. We conclude that although the CMD data do not mandate the existence of a foreground population, they are entirely consistent with a foreground population associated with the LMC that contributes significantly (∼50%) to the observed microlensing optical depth. From our new data, we conclude that ≲40% of the VRC stars are young, massive red clump stars, because (1) synthetic CMDs created using the star formation history derived independently from Hubble Space Telescope data suggest that fewer than 50% of the VRC stars are young, massive red clump stars, (2) the angular distribution of the VRC stars is more uniform than that of the young (
• Zaritsky, D., Thompson, I. M., Harris, J., & Grebel, E. K. (1999). The Magellanic Clouds Photometric Survey. Symposium - International Astronomical Union, 190, 320-323. doi:10.1017/s007418090011811x
  More info

  We present a brief description of the Magellanic Clouds Photometric Survey. In particular, we discuss examples of how the new generation of densely populated CMDs provide new information than that available previously.
• Zaritsky, D., Thompson, I. M., Harris, J., & Grebel, E. K. (1999). The Star Formation History of the Magellanic Clouds: A Preliminary Report. Symposium - International Astronomical Union, 190, 347-348. doi:10.1017/s0074180900118182
  More info

  We present a method to determine the star formation history (SFH) of a mixed stellar population, based on an iterative maximum Likelihood comparison of stellar photometry to model color-magnitude diagrams. We demonstrate the algorithm on a subregion of the Large Magellanic Cloud, observed as part of our ongoing Magellanic Clouds Photometric Survey. We will eventually perform this analysis on hundreds of regions in both Clouds, resulting in a homogeneous SFH map of these galaxies.
• Hunsberger, S. D., Charlton, J. C., & Zaritsky, D. (1998). The luminosity function of galaxies in compact groups. ASTROPHYSICAL JOURNAL, 505(2), 536-557.
• Hunsberger, S. D., Charlton, J. C., & Zaritsky, D. (1998). The luminosity function of galaxies in compact groups. Astrophysical Journal Letters, 505(2 PART I), 536-557.
  More info

  Abstract: From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts to determine a luminosity function extending to MR = -14.0+5 log h75, approximately 2 mag deeper than previous compact group luminosity functions. We find that a single Schlechter function is a poor fit (χv2 > 4) to the data, so we fit a composite function consisting of separate Schechter functions for the bright and faint galaxies. The bright end is best fit with M* = -21.6 and α = -0.52, and the faint end with Mα = -16.1 and α = -1.17. The decreasing bright-end slope implies a deficit of intermediate-luminosity galaxies in our sample of HCGs, and the faint-end slope is slightly steeper than that reported for earlier HCG luminosity functions. Furthermore, luminosity functions of subsets of our sample reveal more substantial dwarf populations for groups with X-ray halos, groups with tidal dwarf candidates, and groups with a dominant elliptical or lenticular galaxy. Collectively, these results support the hypothesis that within compact groups, the initial dwarf galaxy population is replenished by "subsequent generations" formed in the tidal debris of giant galaxy interactions. © 1998. The American Astronomical Society. All rights reserved.
• Nelson, A. E., Zaritsky, D., & Cutri, R. M. (1998). A direct detection of dust in the outer disks of nearby galaxies. Astronomical Journal, 115(6), 2273-2284.
  More info

  Abstract: We measure the extent of 100 μm galactic emission in two independent galaxy samples using the IRAS 100 μm Sky Survey images and constrain the distribution of dust at large (≲30 kpc) radii. The first sample consists of 90 nearby (v < 6000 km s-1) galaxies from the Third Reference Catalogue of Bright Galaxies with similar angular sizes and absolute luminosities (5′ ≤ D25 ≤ 10′ and -22.5 ≤ MB ≤ -18) that are isolated in the 100 μm images. The second sample consists of 24 local galaxies (v < 1500 km s-1, 10′ ≤ D25 ≤ 30′). We rescale the 100 μm images of these galaxies using their optical diameters, D25, rotate the images using their optical major-axis position angle, construct the mean and median images, and rebin the final images into polar coordinates to study the 100 μm emission as a function of radius and azimuthal angle. We find that the 100 μm emission extends at least to radii of 33 kpc (2 σ detection) for the typical galaxy in the 5′-10′ sample and to 21 kpc (2 σ detection) in the 10′-30′ sample (H0 = 75 km s-1 Mpc-1). In both samples, the emission is preferentially elongated along the optical major axis. We fit an exponential to the 100 μm emission along the major axis and measure a scale length of 2.5 ± 0.8 kpc (90% confidence interval). Using a simple model that relates the far-IR emission to the stellar distribution, we examine the range of acceptable dust mass distributions allowed by our data and conclude that the dust is more extended than the starlight.
• Smith, R. C., Bregman, J., Chu, Y. -., Ciardullo, R., Jacoby, G., Kennicutt, R., Oey, S., Winkler, F., & Zaritsky, D. (1998). The UM/CTIO magellanic cloud emission-line survey. Publications of the Astronomical Society of Australia, 15(1), 163-164.
  More info

  Abstract: The Magellanic Clouds are unique in providing us with sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [SII], and [OIII]. The emission-line images will be used in detailed optical and multiwavelength studies of HII regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (∼1 pc) all the way up to global scales.
• Stanek, K. Z., Zaritsky, D., & Harris, J. (1998). A "short" distance to the large magellanic cloud with the Hipparcos calibrated red clump stars. ASTROPHYSICAL JOURNAL, 500(2), L141-L144.
• Stanek, K. Z., Zaritsky, D., & Harris, J. (1998). A "short" distance to the large magellanic cloud with the Hipparcos calibrated red clump stars. Astrophysical Journal Letters, 500(2 PART II), L141-L144.
  More info

  Abstract: Following an approach developed by Paczyński & Stanek, we derive a distance to the Large Magellanic Cloud (LMC) by comparing red clump stars from the Hipparcos catalog with the red clump stars observed in two fields in the LMC that were selected from the ongoing photometric survey of the Magellanic Clouds to lie in low-extinction regions. The use of red clump stars allows a single step determination of the distance modulus to the LMC, μ0.LMC = 18.065 ± 0.031 ± 0.09 mag (statistical plus systematic error), and the corresponding distance, RLMC = 41.02 ± 0.59 ± 1.74 kpc. This measurement is in excellent agreement with the recent determination by Udalski et al., also based on the red clump stars, but is ∼0.4 mag smaller than the generally accepted value of μ0.LMC = 18.50 ± 0.15 mag. We discuss possible reasons for this discrepancy and how it can be resolved. © 1998. The American Astronomical Society. All rights reserved.
• Gordon, K. D., Meixner, M., Meade, M. R., Whitney, B., Engelbracht, C., Bot, C., Boyer, M. L., Lawton, B., Sewilo, M., Babler, B., Bernard, J. -., Bracker, S., Block, M., Blum, R., Bolatto, A., Bonanos, A., Harris, J., Hora, J. L., Indebetouw, R., , Misselt, K., et al. (1997). SURVEYING THE AGENTS OF GALAXY EVOLUTION IN THE TIDALLY STRIPPED, LOW METALLICITY SMALL MAGELLANIC CLOUD (SAGE-SMC). I. OVERVIEW. ASTRONOMICAL JOURNAL, 142(4).
• Harris, J., & Zaritsky, D. (1997). A method for determining the star formation history of a mixed stellar population. ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 136(1), 25-40.
• Harris, J., Zaritsky, D., & Thompson, I. (1997). On the distribution of dust in the Large Magellanic Cloud. ASTRONOMICAL JOURNAL, 114(5), 1933-&.
• Harris, J., Zaritsky, D., & Thompson, I. (1997). On the distribution of dust in the large magellanic cloud. Astronomical Journal, 114(5), 1933-1944.
  More info

  Abstract: We present a detailed map of the reddening in a 1.9° × 1.5° section of the Large Magellanic Cloud (LMC), constructed from UBVI photometry of 2069 O and B main sequence stars. We use two reddening-free photometric parameters to determine the line-of-sight reddening to these stars. We find a mean reddening, 〈E(B-V)〉LMC=0.20 mag, with a non-Gaussian tail to high values. When the reddening is corrected for foreground Galactic extinction (Oestreicher et al. 1995, A&AS, 112, 495), we find 〈E(B-V)〉LMC=0.13 mag. The line-of-sight values are then interpolated onto a uniform grid with a local least-squares plane fitting routine to construct a reddening map of the region. We use the distribution of reddening values to constrain the line-of-sight geometry of stars and dust in the LMC, and to test and normalize a standard extinction correction for galaxy photometry. We attempt to distinguish between line-of-sight depth effects and structure in the dust distribution as possible causes for the observed differential reddening through this region. We conclude: (1) that our data are consistent with a vertical exponential distribution of stars and dust in the LMC, for which the dust scale height is twice that of the OB stars; (2) that the dust distribution must be non-uniform (clumpy) to account for the full distribution of measured reddening values (i.e., line-of-sight effects alone are insufficient to explain the observed structure); and (3) that the B-band optical depth, τB, through the observed region of the LMC is 0.69
• Weisz, D. R., Dalcanton, J. J., Williams, B. F., Gilbert, K. M., Skillman, E. D., Seth, A. C., Dolphin, A. E., McQuinn, K. B., Gogarten, S. M., Holtzman, J., Rosema, K., Cole, A., Karachentsev, I. D., & Zaritsky, D. (1997). THE ACS NEARBY GALAXY SURVEY TREASURY. VIII. THE GLOBAL STAR FORMATION HISTORIES OF 60 DWARF GALAXIES IN THE LOCAL VOLUME. ASTROPHYSICAL JOURNAL, 739(1).
• ZARITSKY, D., ELSTON, R., & HILL, J. (1997). KINEMATICS AND COMPOSITION OF H-II REGIONS IN SPIRAL GALAXIES .1. M33. ASTRONOMICAL JOURNAL, 97(1), 97-106.
• Zaritsky, D., & Lin, D. N. (1997). Evidence for an intervening stellar population toward the large magellanic cloud. Astronomical Journal, 114(6), 2545-2555.
  More info

  Abstract: We identify a vertical extension of the red clump stars in the color magnitude diagram (CMD) of a section of the Large Magellanic Cloud (LMC). The distribution of stars in this extension is indistinguishable in the U, B, V, and I bands - confirming that the detection is real and placing a strong constraint on models of this stellar population. After subtracting the principal red clump component, we find a peak in the residual stellar distribution that is ∼ 0.9 mag brighter than the peak of the principal red clump distribution. We consider and reject the following possible explanations for this population: inhomogeneous reddening, Galactic disk stars, random blends of red clump stars, correlated blends of red clump stars (binaries), evolution of the red clump stars, and red clump stars from a younger LMC stellar population. Combinations of these effects cannot be ruled out as the origin of this stellar population A natural interpretation of this new population is that it consists of red clump stars that are closer to us than those in the LMC. We derive a distance for this population of ∼ 33 to 35 kpc, although the measurement is sensitive to the modeling of the LMC red clump component. We find corroborating evidence for this interpretation in Holtzman et al. s (1997, AJ, 113, 656) Hubble Space Telescope CMD of the LMC field stars. The derived distance and projected angular surface density of these stars relative to the LMC stars (≲ 5 to 7%) are consistent with (1) models that attribute the observed microlensing lensing optical depth (Alcock et al. 1997, ApJ, 486, 697) to a distinct foreground stellar population (Zhao 1997, preprint, astro-ph/9703097) and (2) tidal models of the interaction between the LMC and the Milky Way (Lin et al. 1995, ApJ, 439, 652). The first result suggests that the Galactic halo may contain few, if any, purely halo MACHO objects. The second result suggests that this new population may be evidence of a tidal tail from the interaction between the LMC and the Galaxy (although other interpretations, such as debris from the LMC-SMC interaction, are possible). We conclude that the standard assumption of a smoothly distributed halo population out to the LMC cannot be substantiated without at least a detailed understanding of several of the following: red clump stellar evolution, binary fractions, binary mass ratios, the spatial correlation of stars within the LMC, possible variations in the stellar populations of satellite galaxies, and differential reddening - all of which are highly complex. © 1997 The American Astronomical Society.
• Zaritsky, D., & Rix, H. (1997). Lopsided spiral galaxies and a limit on the galaxy accretion rate. Astrophysical Journal Letters, 477(1 PART I), 118-127.
  More info

  Abstract: We present a measurement of lopsidedness for the stellar disks of 60 field spiral galaxies in terms of the azimuthal m = 1 Fourier amplitude, A1, of the stellar light. We confirm the previous result (Rix & Zaritsky) that ∼30% of field spiral galaxies in a magnitude-limited sample exhibit significant lopsidedness (〈A1/A0〉 ≥ 0.2) at large radii (R > 1.5 disk scalelengths). We conjecture that this lopsidedness is caused by tidal interactions and calculate an upper limit on the accretion rate of small galaxies. We exploit the correlation between lopsidedness and photometric measures of recent star formation (Zaritsky) to obtain two independent estimates of the lifetime of these m = 1 distortions. First, we show that lopsided galaxies have an excess of blue luminosity relative to that of symmetric galaxies with the same H I linewidth, which we attribute to a recent star formation episode that was triggered by an interaction between the galaxy and a companion. We use stellar population models (Bruzual & Chariot) to estimate the time since that interaction. Second, we use the N-body simulation of an infalling satellite by Walker, Mihos, & Hernquist to estimate how fast tidally induced m = 1 distortions are erased through phase mixing. Both approaches indicate that the observations are consistent with a hypothesized tidal interaction that occurred about 1 Gyr ago for galaxies that are lopsided at the 20% level. By combining this lifetime estimate for lopsidedness, the observed frequency of such distortions, and a correction to the survey volume that depends on the increase in luminosity during an interaction, we derive an upper limit on the current companion accretion rate of field spiral galaxies (for companion masses ~10% parent galaxy mass) that lies in the range 0.07-0.25 Gyr-1. The principal uncertainty in this limit arises from ambiguities in the interpretation of the correlation between lopsidedness and MB. © 1997. The American Astronomical Society. All rights reserved.
• Zaritsky, D., Harris, J., & Thompson, I. (1997). A digital photometric survey of the magellanic clouds: First results from one million stars. Astronomical Journal, 114(3), 1002-1013.
  More info

  Abstract: We present the first results from, and a complete description of, our ongoing UBVI digital photometric survey of the Magellanic Clouds. In particular, we discuss the photometric quality and automated reduction of a CCD survey (magnitude limits, completeness, and astrometric accuracy) that covers the central 8° × 8° of the Large Magellanic Cloud (LMC) and 4° × 4° of the Small Magellanic Cloud (SMC). We discuss photometry of over 1 million stars from the initial survey observations (an area northwest of the LMC bar covering ∼2° × 1.5°) and present a deep stellar cluster catalog that contains about 45% more clusters than previously identified within this region. Of the 68 clusters found, only 12 are also identified as concentrations of "old," red clump stars. Furthermore, only three clusters are identified solely on the basis of a concentration of red clump stars, rather than as a concentration of luminous (V
• Zaritsky, D., Nelson, A. E., Dalcanton, J. J., & Gonzalez, A. H. (1997). Distant galaxy clusters identified from optical background fluctuations. ASTROPHYSICAL JOURNAL, 480(2), L91-&.
• Zaritsky, D., Nelson, A. E., Dalcanton, J. J., & Gonzalez, A. H. (1997). Distant galaxy clusters identified from optical background fluctuations. Astrophysical Journal Letters, 480(2 PART II), L91-L94.
  More info

  Abstract: We present the first high-redshift (0.3 < z < 1.1) galaxy clusters found by systematically identifying optical low surface brightness fluctuations in the background sky. Using spectra obtained with the Keck I telescope and I-band images from the Palomar 1.5 m telescope, we conclude that at least eight of the 10 candidates examined are high-redshift galaxy clusters. The identification of such clusters from low surface brightness fluctuations provides a complement to classic selection methods based on overdensities of resolved galaxies and enables us to search efficiently for rich high-redshift clusters over large areas of the sky. The detections described here are the first in a survey that covers a total of nearly 140 deg2 of the sky and should yield, if these preliminary results are representative, over 300 such clusters. © 1997. The American Astronomical Society. All rights reserved.
• Zaritsky, D., Smith, R., Frenk, C. S., & White, S. (1997). Anisotropies in the distribution of satellite galaxies. ASTROPHYSICAL JOURNAL, 478(2), L53-L56.
• Zaritsky, D., Smith, R., Frenk, C. S., & White, S. D. (1997). Anisotropies in the distribution of satellite galaxies. Astrophysical Journal Letters, 478(2 PART II), L53-L56.
  More info

  Abstract: We find that satellites of isolated disk galaxies at projected radii between 300 and 500 kpc are distributed asymmetrically about the parent galaxy and aligned preferentially with the disk minor axis. The dynamical timescale at these radii is sufficiently long that the shape of this distribution must reflect the formation history of the outer halo rather than its internal evolution. We also find that the orbital angular momenta of satellites at projected major axis distances of ≲ 200 kpc tend to align with that of the central disk. These results demonstrate that satellites are dynamically related to their primary galaxy. Satellites drawn from current simulations of hierarchical galaxy formation exhibit neither the systematic alignment nor the net rotation with the central disk that we find in the data. © 1997. The American Astronomical Society. All rights reserved.
• Zaritsky, D., Smith, R., Frenk, C., & D., S. (1997). More satellites of spiral galaxies. Astrophysical Journal Letters, 478(1 PART I), 39-48.
  More info

  Abstract: We present a revised and expanded catalog of satellite galaxies of a set of isolated spiral galaxies similar in luminosity to the Milky Way. This sample of 115 satellites, 69 of which were discovered in our multifiber redshift survey, is used to probe the results obtained from the original sample further (Zaritsky et al.). The satellites are, by definition, at projected separations lsim;500 kpc, have absolute recessional velocity differences with respect to the parent spiral of less than 500 km s-1, and are at least 2.2 mag fainter than their associated primary galaxy. A key characteristic of this survey is the strict isolation of these systems, which simplifies any dynamical analysis. We find no evidence for a decrease in the velocity dispersion of the satellite system as a function of radius out to galactocentric radii of 400 kpc, which suggests that the halo extends well beyond 200 kpc. Furthermore, the new sample affirms our previous conclusions (Zaritsky et al.) that (1) the velocity difference between a satellite and its primary is not strongly correlated with the rotation speed of the primary, (2) the system of satellites has a slight net rotation (34 ± 14 km s-1) in the same sense as the primary's disk, and (3) that the halo mass of an ∼L* spiral galaxy is in excess of 2 × 1012 M⊙. © 1997. The American Astronomical Society. All rights reserved.
• Hunsberger, S. D., Charlton, J. C., & Zaritsky, D. (1996). The formation of dwarf galaxies in tidal debris: A study of the compact group environment. Astrophysical Journal Letters, 462(1 PART I), 50-56.
  More info

  Abstract: From R-band images of 42 Hickson compact groups, we present a sample of 47 candidate dwarf galaxies that are associated with the tidal tails and arms in the groups. The candidates, found in 15 tidal features, have R magnitudes and masses (for M/L = 1) in the ranges -16.5 ≤ MR -5 log h75 ≤ -11.5 and 2 × 106 M⊙; ≤ M ≤ 2 × 108 M⊙, respectively. Their masses and locations are compared to the predictions of theoretical/N-body tidal dwarf formation scenarios. Considering the longevity of tidal debris in the compact group environment and the results of this survey, we estimate the contribution of the tidal dwarf formation mechanism to the population of dwarf galaxies observed at large in compact groups. If the majority of our dwarf galaxy candidates are confirmed as being gravitationally bound stellar systems, then a significant fraction, perhaps as much as one-half, of the dwarf population in compact groups is the product of interactions among giant parent galaxies. © 1996. The American Astronomical Society. All rights reserved.
• Knierman, K., Gallagher, S., Charlton, J., Hunsberger, S., Whitmore, B., Kundu, A., Hibbard, J., & Zaritsky, D. (1996). From globular clusters to tidal dwarfs: Structure formation in the tidal tails of merging galaxies. ASTRONOMICAL JOURNAL, 126(3), 1227-1244.
• Kobulnicky, H., & Zaritsky, D. (1996). Chemical properties of star-forming emission-line galaxies at z = 0.1-0.5. ASTROPHYSICAL JOURNAL, 511(1), 118-135.
• Poggianti, B. M., Aragon-Salamanca, A., Zaritsky, D., De Lucia, G., Milvang-Jensen, B., Desai, V., Jablonka, P., Halliday, C., Rudnick, G., Varela, J., Bamford, S., Best, P., Clowe, D., Noll, S., Saglia, R., Pello, R., Simard, L., von der Linden, A., & White, S. (1996). THE ENVIRONMENTS OF STARBURST AND POST-STARBURST GALAXIES AT z=0.4-0.8. ASTROPHYSICAL JOURNAL, 693(1), 112-131.
• Skillman, E. D., Kennicutt Jr., R. C., Shields, G. A., & Zaritsky, D. (1996). Chemical abundances in Virgo spiral galaxies. II. Effects of cluster environment. Astrophysical Journal Letters, 462(1 PART I), 147-162.
  More info

  Abstract: We present new measurements of chemical abundances in H II regions in spiral galaxies of the Virgo cluster and a comparison of Virgo galaxies and field spirals. With these new data there now exist nine Virgo spirals with abundance measurements for at least four H II regions. Our sample of Virgo galaxies ranges from H I deficient objects near the core of the cluster to galaxies with normal H I properties, far from the cluster core. We investigate the relationship between H I disk characteristics and chemical abundances to determine whether dynamical processes that remove gas from the disk, such as ram pressure stripping by the intracluster medium, also affect the chemical abundances. We divide the nine Virgo spirals into three groups of three galaxies each: those with strong H I deficiencies, intermediate cases, and those with no H I deficiencies. The three most H I deficient Virgo spirals have larger mean abundances (0.3 to 0.5 dex in O/H) than the spirals on the periphery of the cluster. This suggests that dynamical processes associated with the cluster environment are more important than cluster membership in determining the current chemical properties of spiral galaxies. There is also weak evidence of shallower abundance gradients in the H I deficient Virgo spirals. We also compare the abundance properties of our Virgo sample to a large sample of field spirals studied by Zaritsky, Kennicutt, & Huchra (1994). Those authors found that the mean abundance of the disk gas increases with increasing maximum circular velocity, increasing luminosity, and decreasing (earlier) Hubble type (but with a large dispersion in the mean abundances and abundance gradients). The dispersion in the properties of field galaxies and the small size of the Virgo sample make it difficult to draw definitive conclusions about any systematic difference between the field and Virgo spirals. Nevertheless, the H I deficient Virgo galaxies have larger mean abundances than field galaxies of comparable luminosity or Hubble type, while the spirals at the periphery of the cluster are indistinguishable from the field galaxies. Simple, illustrative chemical evolution models with infall of metal-poor gas are constructed and compared to models in which the infall is terminated. The models are constrained by comparison with observed gas mass fractions, current star formation rates, and gas consumption times. The model results indicate that the curtailment of infall of metal-poor gas onto cluster core spirals may explain part of the enhanced abundance. However, additional work is needed, particularly modeling of the effects of truncating the outer gaseous disk within the context of models with radial gas transport. The increased abundances in cluster core late-type spirals, relative to field galaxies, may be important in the interpretation of observations of these galaxies. Specifically, we point to possible effects on the Tully-Fisher and Cepheid variable distance determinations and the interpretation of colors in the Butcher-Oemler effect. © 1996. The American Astronomical Society. All rights reserved.
• Thompson, I. M., Harris, J., Zaritsky, D., Thompson, I. B., Smith, R. C., Mateo, M., Hodge, P. W., & Harris, J. (1996). A drift-scan photometric survey of the Magallanic Clouds.. Bulletin of the American Astronomical Society, 28(2).
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., Tucker, D. L., Shectman, S. A., Oemler, A., Lin, H., Kirshner, R. P., Kirhner, R. P., & Hashimoto, Y. (1996). The environment of "E+A" galaxies. The Astrophysical Journal, 466, 104-113. doi:10.1086/177495
• Zaritsky, D., Schectman, S. A., & Bredthauer, G. (1996). THE GREAT-CIRCLE CAMERA: A NEW DRIFT-SCANNING INSTRUMENT. Publications of the Astronomical Society of the Pacific, 108(719), 104-109. doi:10.1086/133698
  More info

  We discuss the design, construction, and use of a new class of scanning camera that eliminates a critical limitation of standard CCD drift-scan observations. A standard scan, which involves no correction for the differential drift rates and curved stellar paths across the field-of-view, suffers from severe image degradation even when one observes at moderate declinations. Not only does this effect limit the area of the sky over which drift scanning is viable, but as detector sizes increase, CCD mosaics become standard, and dome/telescope seeing improves, the area of sky for which scanning is acceptable (image degradation
• Zaritsky, D., Shectman, S. A., & Bredthauer, G. (1996). The great circle camera: A new drift-scanning instrument. PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 108(719), 104-109.
• Zaritsky, D., Shectman, S. A., & Bredthauer, G. (1996). The great circle camera: A new drift-scanning instrument. Publications of the Astronomical Society of the Pacific, 108(719), 104-109.
  More info

  Abstract: We discuss the design, construction, and use of a new class of scanning camera that eliminates a critical limitation of standard CCD drift-scan observations. A standard scan, which involves no correction for the differential drift rates and curved stellar paths across the field of view, suffers from severe image degradation even when one observes at moderate declinations. Not only does this effect limit the area of the sky over which drift scanning is viable but, as detector sizes increase, CCD mosaics become standard, and dome/telescope seeing improves, the area of sky for which scanning is acceptable (image degradation ≲ seeing) will be further reduced unless some action is taken. By modifying the scan path (the path on the sky traced by signal accumulated along a single CCD column) to lie along a great circle on the sky rather than along a path of constant declination, image degradation is minimized. In this paper, we discuss the design and implementation of a stage that rotates and translates the CCD during a drift-scan exposure so that the scan path is along a great circle on the sky. Data obtained during the commissioning run of the Great Circle Camera at the Las Campanas 1-m telescope are presented.
• Rix, H., & Zaritsky, D. (1995). Nonaxisymmetric structures in the stellar disks of galaxies. Astrophysical Journal Letters, 447(1), 82-102.
  More info

  Abstract: We study the azimuthal structure of the stellar disks of 18 face-on spiral galaxies, using K′(2.2 μm)-band photometry to trace the stellar surface mass density. Assuming the disks are coplanar, we characterize their deviation from axisymmetry by the fractional amplitudes, Am(R)/A0(R), and phases, φm(R), of the mth azimuthal Fourier components at radii R about the photometric galaxy center. We find that most disks exhibit a wealth of nonaxisymmetric structures, specifically (1) that about one-third of them are substantially lopsided (A1/A0 ≳ 0.20) at 2.5 disk exponential scale length, (2) that almost half of them have strong two-armed spirals with an arm/interarm surface-brightness contrast of order unity, and (3) that typical disks have some intrinsic ellipticity. We estimate that in the disk plane the characteristic ellipticity of the underlying potential is 0.045+0.03-0.02. However, the spiral pattern couples significantly to the estimate of the intrinsic ellipticity, and our measurement may represent an upper limit on the "true" potential triaxiality. We estimate the radial streaming motions of the disk stars, vR, which are produced by these distortions. By averaging over our sample of galaxies and all azimuthal angles, we find 〈vR〉 ∼ 7 km s-1 due to lopsided distortions and 〈vR〉 ∼ 6 km s-1 due to intrinsic ellipticity. These noncircular motions are expected to contribute ∼0.15 mag scatter to measurements of the Tully-Fisher relation.
• Sheth, K., Regan, M., Hinz, J. L., de Paz, A. G., Menendez-Delmestre, K., Munoz-Mateos, J., Seibert, M., Kim, T., Laurikainen, E., Salo, H., Gadotti, D. A., Laine, J., Mizusawa, T., Armus, L., Athanassoula, E., Bosma, A., Buta, R. J., Capak, P., Jarrett, T. H., , Elmegreen, D. M., et al. (1995). The Spitzer Survey of Stellar Structure in Galaxies (S(4)G). PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF THE PACIFIC, 122(898), 1397-1414.
• Shields, G. A., Skillman, E. D., Kennicutt Jr., R. C., & Zaritsky, D. (1995). High chemical abundances in H I deficient spirals of the virgo cluster. Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias, 3, 149-152.
  More info

  Abstract: New spectroscopic observations of H II regions, together with published data, are used to derive interstellar O abundances in 9 late-type spiral galaxies in the Virgo cluster. The galaxies are divided into 3 groups according to their deficiency of H I relative to normal field spirals. Generally, the most H I deficient galaxies are closest to the cluster core. The outlying spirals with normal H I content show abundances and radial abundance gradients similar to those in field spirals. The H I deficient galaxies show abundances larger by about 0.3 dex and relatively flat radial gradients. The galaxies with an intermediate degree of H I deficiency are intermediate in O abundance. These results confirm and clarify earlier indications that spirals evolve to higher chemical abundances in the cluster environment. Simple chemical evolution models indicate that curtailment of infall into spirals in the cluster core may explain part of the abundance differential, but there appears to be a need for other mechanisms. © Universidad Nacional Autónoma de México.
• White, S., Clowe, D., Simard, L., Rudnick, G., De Lucia, G., Aragon-Salamanca, A., Bender, R., Best, P., Bremer, M., Charlot, S., Dalcanton, J., Dantel, M., Desai, ., Fort, B., Halliday, C., Jablonka, P., Kauffmann, G., Mellier, Y., Milvang-Jensen, B., , Pello, R., et al. (1995). EDisCS - the ESO distant cluster survey - Sample definition and optical photometry. ASTRONOMY & ASTROPHYSICS, 444(2), 365-U27.
• ZABLUDOFF, A. I., & ZARITSKY, D. (1995). A COLLISION OF SUBCLUSTERS IN ABELL-754. ASTROPHYSICAL JOURNAL, 447(1), L21-L24.
• Zabludoff, A. I., Zaritsky, D., & Zabludoff, A. I. (1995). A collision of subclusters in Abell 754. The Astrophysical Journal, 447(1). doi:10.1086/309552
  More info

  We present direct evidence of a collision of subclusters in the galaxy cluster Abell 754. Our comparison of new optical data and archival ROSAT PSPC X-ray data reveals three collision signatures predicted by n-body/hydrodynamical simulations of hierarchical cluster evolution. First, there is strong evidence of a nonhydrostatic process; neither of the two major clumps in the galaxy distribution lies on the off-center peak of the X-ray emission from the intracluster gas. Second, the peak of the X-ray emission is elongated perpendicular to the collision axis defined by connecting the centroids of the two galaxy clumps. Third, there is evidence of compression-heated gas; one of A754's two X-ray temperature components (Henry & Briel 1995) is among the hottest observed in any cluster and hotter than that inferred from the velocity dispersion of the associated galaxy clump. These signatures are consistent with the qualitative features of simulations (Evrard 1990a, b) in which two subclusters have collided in the plane of the sky during the last ~1 Gyr. The detection of such collisions is crucial for understanding both the dynamics of individual clusters and the underlying cosmology. First, for systems like A754, estimating the cluster X-ray mass from assumptions of hydrostatic equilibrium and isothermality is incorrect and may produce the discrepancies sometimes found between X-ray masses and those derived from gravitational lens models (Babul & Miralda-Escude 1994). Second, the fraction of nearby clusters in which subclusters have collided in the last ~1 Gyr is especially sensitive to the mean mass density parameter Ω0 (see Richstone, Loeb, & Turner 1992; Evrard et al. 1993; Lacey & Cole 1993). As we show for A754, we now have the means to identify recent collisions. With a large, well-defined cluster sample, it will be possible to place a new and powerful constraint on cosmological models.
• Zabludoff, A. I., Zaritsky, D., Zabludoff, A. I., & Willick, J. A. (1995). Spectral classification of galaxies along the hubble sequence. The Astronomical Journal, 110(4), 1602-1613. doi:10.1086/117634
  More info

  We develop a straightforward and quantitative two-step method for spectroscopically classifying galaxies from the low signal-to-noise (S/N) optical spectra typical of galaxy redshift surveys. First, using \chi^2-fitting of characteristic templates to the object spectrum, we determine the relative contributions of the old stellar component, the young stellar component, and various emission line spectra. Then, we classify the galaxy by comparing the relative strengths of the components with those of galaxies of known morphological type. In particular, we use the ratios of (1) the emission line to absorption line contribution, (2) the young to old stellar contribution, and (3) the oxygen to hydrogen emission line contribution. We calibrate and test the method using published morphological types for 32 galaxies from the long-slit spectroscopic survey of Kennicutt (1992) and for 304 galaxies from a fiber spectroscopic survey of nearby galaxy clusters. From an analysis of a sample of long-slit spectra of spiral galaxies in two galaxy clusters, we conclude that the majority of the galaxies observed in the fiber survey are sufficiently distant that their spectral classification is unaffected by aperture bias. Our spectral classification is consistent with the morphological classification to within one type (e.g. E to S0 or Sa to Sb) for \gtsim 80% of the galaxies. Disagreements between the spectral and morphological classifications of the remaining galaxies reflect a divergence in the correspondence between spectral and morphological types, rather than a problem with the data or method.
• Zaritsky, D. (1995). Evidence for recent accretion in nearby galaxies. Astrophysical Journal Letters, 448(1 PART 2), L17-L20.
  More info

  Abstract: I discuss observations of magnitude residuals from the B-band Tully-Fisher relationship, B - V color, chemical abundance gradients, and asymmetries in the H I and stellar disks of nearby spiral galaxies within the context of a model in which small satellites or H I clouds are accreted onto the outer disks of spiral galaxies. Correlations between the various observables support the hypothesis that accretion dilutes the gas-phase abundances in the outer disk, steepens the abundance gradient across the disk, increases the star formation rate, and creates asymmetries in the outer disk. By estimating the duration of steep abundance gradients, elevated rates of star formation, or outer disk asymmetries, we can place constraints on the rate of accretion events. The data suggest that accretion events at the current time are common.
• Clowe, D., Schneider, P., Aragon-Salamanca, A., Bremer, M., De Lucia, G., Halliday, C., Jablonka, P., Milvang-Jensen, B., Pello, R., Poggianti, B., Rudnick, G., Saglia, R., Simard, L., White, S., & Zaritsky, D. (1994). Weak lensing mass reconstructions of the ESO Distant Cluster Survey. ASTRONOMY & ASTROPHYSICS, 451(2), 395-U22.
• LORRIMER, S. J., FRENK, C. S., SMITH, R. M., WHITE, S., & ZARITSKY, D. (1994). THE DISTRIBUTION OF SATELLITE GALAXIES. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 269(3), 696-706.
• ZARITSKY, D., KENNICUTT, R., & HUCHRA, J. (1994). H-II REGIONS AND THE ABUNDANCE PROPERTIES OF SPIRAL GALAXIES. ASTROPHYSICAL JOURNAL, 420(1), 87-109.
• ZARITSKY, D., OLSZEWSKI, E., SCHOMMER, R., PETERSON, R., & AARONSON, M. (1994). VELOCITIES OF STARS IN REMOTE GALACTIC SATELLITES AND THE MASS OF THE GALAXY. ASTROPHYSICAL JOURNAL, 345(2), 759-769.
• Zaritsky, D. (1994). Preliminary evidence for dust in galactic halos. Astronomical Journal, 108(5), 1619-1626.
  More info

  Abstract: I use B and I photometry of distant galaxies observed through the halos of two nearby spiral galaxies, NGC 2835 and NGC 3521, to test for the existence of dust in galactic halos out to at least a radius of 60 kpc. B-I colors of background galaxies in fields centered along the nearby galaxy's major axis at a projected separation of 60 kpc are compared to the colors of background galaxies in fields centered at a projected separation of about 220 kpc. Background galaxies in the fields at smaller projected separations have average B-I colors that are 0.067±0.033 mag redder than those in the outer fields. Such a result will occur by chance less than 2.2% of the time and so is taken as preliminary evidence that galaxy halos contain more dust at galactic radii of 60 than 220 kpc. A model which assumes that the radial dust profile in galactic disks and halos is a single exponential has a corresponding scale length of 31±8 kpc. I argue on the basis of the IRAS 100 μm flux maps that absorption by Galactic dust is not responsible for this result and briefly discuss connections between this result and other observations of the baryonic component of galaxy halos.
• Zaritsky, D., & White, S. D. (1994). The massive halos of spiral galaxies. Astrophysical Journal Letters, 435(2), 599-610.
  More info

  Abstract: We use the sample of satellite galaxies presented by Zaritsky et al. (1993) to demonstrate the existence of extended massive dark halos around spiral galaxies. Isolated spirals with rotation velocities near 250 km s-1 have a typical halo mass within 200 kpc of 1.5-2.6 × 1012 M⊙ (90% confidence range for H0 = 75 km s-1 Mpc-1). This result is most easily derived using standard mass estimator techniques, but such techniques do not account for the strong observational selection effects in the sample, nor for the extended mass distributions that the data imply. These complications can be addressed using scale-free models similar to those previously employed to study binary galaxies. When satellite velocities are assumed isotropic, both methods imply massive and extended halos. However, the derived masses depend sensitively on the assumed shape of satellite orbits. Furthermore, both methods ignore the fact that many of the satellites in the sample have orbital periods comparable to the Hubble time. The orbital phases of such satellites cannot be random, and their distribution in radius cannot be freely adjusted; rather these properties reflect ongoing infall onto the outer halos of their primaries. We use detailed dynamical models for halo formation to evaluate these problems, and we devise a maximum likelihood technique for estimating the parameters of such models from the data. The most strongly constrained parameter is the mass within 200-300 kpc, giving the confidence limits quoted above. The eccentricity, e, of satellite orbits is also strongly constrained, 0.50 < e < 0.88 at 90% confidence, implying a near-isotropic distribution of satellite velocities. The cosmic density parameter in the vicinity of our isolated halos exceeds 0.13 at 90% confidence, with preferred values exceeding 0.3.
• Zaritsky, D., Kennicutt Jr., R. C., & Huchra, J. P. (1994). H II regions and the abundance properties of spiral galaxies. Astrophysical Journal Letters, 420(1), 87-109.
  More info

  Abstract: We investigate the relationships between the characteristic oxygen abundance, the radial abundance gradient, and the macroscopic properties of spiral galaxies by examining the properties of individual H II regions within those galaxies. Our observations of the line flux ratio ([O II] λλ3726, 3729 + [O III] λλ4959, 5007)/Hβ for 159 H II regions in 14 spiral galaxies are combined with published data to provide a sample of 39 disk galaxies for which ([O II] + [O III])/Hβ has been measured for at least five H II regions. We find that the characteristic gas-phase abundances and luminosities of spiral galaxies are strongly correlated. This relationship maps almost directly onto the luminosity-metallicity relationship of irregular galaxies and is also quite similar to that found for elliptical and dwarf spheroidal galaxies. Within our sample of spirals, a strong correlation between characteristic abundance and Hubble type also exists. The correlation between luminosity and Hubble type complicates the issue, but we discuss several interpretations of the correlations. The relationship between circular velocity and characteristic abundance is also discussed. We find that the slopes of the radial abundance gradients, when expressed in units of dex/isophotal radius, do not significantly correlate with either luminosity or Hubble type. However, the hypothesis that both early and very late type spirals have shallower gradients than intermediate spirals is consistent with the data. We find suggestive evidence that the presence of a bar induces a flatter gradient and also briefly discuss whether abundance gradients are exponential, as is usually assumed. We investigate the properties of individual H II regions in a subset of 42 regions for which we have spectra that cover almost the entire spectral range from 3500 to 9800 Å. We use those data to estimate the densities and ionizing spectra within the H II regions. We confirm that the ionizing spectrum hardens with increasing radius and decreasing abundance. We find no correlation between the ionization parameter and either radius or abundance, but this may be due to significant scatter introduced by the simple conversion of line ratios to ionization parameter.
• Zaritsky, D., White, S. D., Smith, R. M., Lorrimer, S. J., & Frenk, C. S. (1994). The distribution of satellite galaxies. Monthly Notices of the Royal Astronomical Society, 269(3), 696-706. doi:10.1093/mnras/269.3.696
• ZARITSKY, D., RIX, H. W., & RIEKE, M. (1993). INNER SPIRAL STRUCTURE OF THE GALAXY M51. NATURE, 364(6435), 313-315.
• Zaritsky, D. (1993). The relationships among mass, metallicity, and morphology for spiral galaxies. Publications of the Astronomical Society of the Pacific, 105(691), 1006-1010. doi:10.1086/133273
  More info

  A brief discussion of recent results on the gas phase oxygen abundance in spiral galaxies is presented. Using those results, I explore the relationship between the characteristic abundance of a galaxy and both its mass and Hubble type. In closing, I speculate about what these relationships may imply for the origin of galaxy morphology.
• Zaritsky, D., Oey, M. S., Kennicutt, R. C., & Huchra, J. P. (1993). Systematics of H II region abundances in galaxies.. Revista Mexicana De Astronomia Y Astrofisica, 27, 21-28.
• Zaritsky, D., Rix, H., & Ricke, M. (1993). Inner spiral structure of the galaxy M51. Nature, 364(6435), 313-315. doi:10.1038/364313a0
  More info

  MODELLING the structure and kinematics of spiral galaxies requires accurate maps of the mass-tracing stellar population. But this has hitherto been difficult because of dust obscuration and the presence of luminous young stars. To minimize the effects of dust and maximize sensitivity to the dominant stellar population, we have obtained K-band (2.2-μm) images of the nearby 'grand-design' spiral galaxy NGC5194 (M51). Our observations reveal remarkable dynamical structures not visible in conventional optical images. We find that the spiral arms extend significantly further towards the galaxy's centre than previously observed and can be traced continuously through almost three revolutions — roughly twice as far as with optical images. The coherence of the arms over this large radial range challenges current theories of spiral structure. We suggest that a combination of several mechanisms, such as the interaction of M51 with the neighbouring galaxy NGC5195, forcing by the central 'bar', or distortions from density waves, is required to generate the observed structure.
• Zaritsky, D., Smith, R., Frenk, C., & D., S. (1993). Satellites of spiral galaxies. Astrophysical Journal Letters, 405(2), 464-478.
  More info

  Abstract: We present a survey of satellites around a homogeneous set of late-type spirals with luminosity similar to that of the Milky Way. The survey aims to probe the mass distribution at galactocentric radii ∼ 250 kpc. The 69 satellites in our sample span a range of magnitudes similar to that of the brighter satellites in the Local Group. Slightly over half the objects are new discoveries. Existing data were supplemented by our observations of radial velocities to obtain km s-1 precision. In this paper we present the data and carry out a first-cut dynamical analysis. On average, we find fewer than 1.5 satellites per primary, but we argue that we can treat the survey as an ensemble and so derive the properties of the halo of a "typical" isolated spiral. The projected density profile of the ensemble falls off approximately as r-1. Within 50 kpc the azimuthal distribution of satellites shows some evidence for the "Holmberg effect," an excess near the minor axis of the primary; however, at larger projected distances, the distribution appears isotropic. There is a weak but significant correlation between the size of a satellite and its distance from its primary, as expected if satellites are tidally truncated. Neither Hubble type nor spectral characteristics correlate with apparent separation. The ensemble of satellites appears to be rotating at about 30 km s-1 in the same direction as the galactic disk. Satellites on prograde orbits tend to be brighter than those on retrograde orbits. The typical velocity difference between a satellite and its primary shows no clear dependence either on apparent separation, or on the rotation speed of the primary. Naive mass estimates suggest that the mass contained within 200 kpc is of order 2 × 1012 M⊙. Thus our survey demonstrates that isolated spiral galaxies have massive halos that extend to many optical radii.
• D., S., & Zaritsky, D. (1992). Models for galaxy halos in an open universe. Astrophysical Journal Letters, 394(1), 1-6.
  More info

  Abstract: We present the properties of simple, self-consistent infall models which embed an " isothermal " dark halo in an open universe. These models depend on one scaling parameter and two shape parameters. The first may be taken to be the circular velocity in the inner regions, and the others to be the density of the universe, Ω, and a measure, e, of the shape of orbits. These models provide a useful description of ensembles of satellite galaxies, or of binary galaxies, because they allow explicitly for the fact that such systems have orbital periods approaching the age of the universe and so cannot have a random orbital phase.
• ZARITSKY, D., SMITH, R., FRENK, C., & WHITE, S. (1992). SATELLITES OF SPIRAL GALAXIES. ASTROPHYSICAL JOURNAL, 405(2), 464-478.
• Zaritsky, D. (1992). The asymmetric distribution of satellite galaxy velocities. Astrophysical Journal Letters, 400(1), 74-79.
  More info

  Abstract: Companion galaxies tend to have redshifts that exceed that of their associated primary. We show that the latest sample of satellite galaxies (from Zaritsky et al.) corroborates this assertion. We examine whether selection biases and contamination by galaxies that are not physical satellites can create the observed velocity asymmetry. As shown by Valtonen and Byrd for previous samples, simple models of the selection process reproduce the sense of the asymmetry, but not its magnitude unless the samples are dominated by interlopers. We expand on this model by using numerical simulations that include a simple model of galaxy clustering, and demonstrate that clustering can increase the magnitude of the expected asymmetry for a particular level of contamination. Depending on input assumptions, these models imply 1 a lower limits on the contamination level in the Zaritsky et al. sample of between 8% and 20%. For an independent estimate of the characteristics of interlopers, we obtained a pure sample of interlopers from the CfA Redshift Catalogue. Using the results from the analysis of that sample and the models, we conclude that, for the type of satellite galaxy sample discussed here, a moderate level of contamination (∼ 10%) is sufficient to account for the observed asymmetry.
• Zaritsky, D. (1992). The dynamics of satellite galaxies.. Publications of the Astronomical Society of the Pacific, 104(672), 155. doi:10.1086/132972
  More info

  We use the positions and velocities of satellites of our galaxy and of other spiral galaxies to determine the radial mass profile of dark matter halos. We combine our measurement of the velocities of five remote Galactic satellites with published observations of the other Galactic satellites to obtain a complete sample of test particles. We then apply statistical techniques and timing arguments to deduce that the mass of the Galaxy is > 1.3 X 1012 solar mass for standard assumptions and that the halo extends beyond 100 kpc Galactocentric distance. We confirm our results by examining the dynamics of other Local Group galaxies. Subsequently, we expand our study to include nearby (1000 km s-1 200 kpc) and massive (> 1012 solar mass), M/L > 80) dark matter halos around isolated unbarred late-type spiral galaxies.
• Zaritsky, D. (1992). The mass of spiral galaxy halos. Publications of the Astronomical Society of the Pacific, 104(679), 831-834. doi:10.1086/133062
  More info

  A brief discussion of previous and current work on the determination of the mass distribution of spiral galaxy halos is presented.
• Zaritsky, D. (1992). The radial distribution of oxygen in disk galaxies. Astrophysical Journal Letters, 390(2 PART 2), L73-L76.
  More info

  Abstract: The shape of the oxygen abundance profile is examined for seven nearby spiral galaxies in which at least 15 H II regions have been observed. The radial abundance profile for three of these galaxies has a distinct change in slope. The others show no deviation from a single scale-length exponential. This behavior is explained within the framework of the star-forming viscous disk model of galaxy evolution. A prediction is made that radial abundance profiles of noninteracting unbarred spiral galaxies change slope at the radius where the rotation curve changes from linearly rising to flat. For barred and interacting galaxies the situation is complicated by additional mixing mechanisms of the interstellar medium.
• ZARITSKY, D., ELSTON, R., & HILL, J. M. (1990). KINEMATICS AND COMPOSITION OF H-II REGIONS IN SPIRAL GALAXIES .2. M51, M101, AND NGC-2403. ASTRONOMICAL JOURNAL, 99(4), 1108-1123.
• Zaritsky, D., & White, S. D. (1990). Determining the Mass of Spiral Galaxy Halos. Bulletin of the American Astronomical Society, 22.
• Zaritsky, D., Elston, R., & Hill, J. M. (1990). Kinematics and composition of H II regions in spiral galaxies. II. M51, M101, and NGC 2403. Astronomical Journal, 99(4), 1108-1123.
  More info

  Abstract: We used the MX multi-object spectrometer to measure the velocities of 103 H II regions in M101 and 32 regions in NGC 2403, and to measure the excitations, log([O III]/Hβ), of 80 regions in M101, 30 in NGC 2403, and 15 in M51. For M101 and NGC 2403 we derive inclinations 17° ± 1° and 58° ± 1°, major-axis position angles 35° ± 1° and 126° ± 1°, rotation curves, line-of-sight velocity dispersions 11 ± 3 and 13 ± 4 km s-1, and mass-to-light ratios in solar units for the optical disks, between 5 and 6 (± 1) for M101 and between 1 and 3 (± 1) for NGC 2403. We demonstrate that late-type spiral galaxies can be divided into two distinct groups based solely on the excitation of their H II regions at a particular fractional isophotal radius. The two groups are analyzed for clues to the cause of the wide variation in excitation. We also discuss excitation variations along the spiral arms of M101 and present evidence that the excitation gradients of M33 and M101 steepen significantly toward the center of the galaxy. Finally, we use the excitation measurements to estimate the magnitude of the abundance gradients in these galaxies. A comparison between our measurement of the abundance gradients in M33, M101, NGC 2403, and NGC 2997 and previous determinations supports our assertion that the abundance gradients obtained by using excitation measurements of more than 30 H II regions per galaxy, are at least as accurate and precise as those presented in the literature. We demonstrate that for late-type spiral galaxies the slope of the abundance gradient correlates with luminosity.
• ZARITSKY, D., ZABLUDOFF, A., & WILLICK, J. (1989). SPECTRAL CLASSIFICATION OF GALAXIES ALONG THE SEQUENCE. ASTRONOMICAL JOURNAL, 110(4), 1602-1613.
• Zabludoff, A., Zaritsky, D., Lin, H., Tucker, D., Hashimoto, Y., Shectman, S., Oemler, A., & Kirshner, R. (1989). The environment of ''E+A'' galaxies. ASTROPHYSICAL JOURNAL, 466(1), 104-+.
• Zaritsky, D., Hill, J. M., & Elston, R. (1989). Kinematics and Composition of H II Regions in Spiral Galaxies. I. M33. The Astronomical Journal, 97, 97. doi:10.1086/114960
  More info

  Moderate-dispersion, 0l.7 A/pixel spectra of H II regions in M33 were taken, and the velocity as well as the excitation were measured by observing the spectral region around H-beta. Velocity measurements for 55 H II regions and excitation measurements for 42 regions are presented. The velocity data are used to measure the systemic velocity at -172 + or - 6 km/s, the inclination at 56 + or - 1 deg, the position angle of the major axis at 23 + or - 1 deg, the rotation curve of the H II regions, and their line-of-sight velocity dispersion at 9 + or - 4 km/s. These data are used to derive the M/L ratio from radii of 0.5-3.7 kpc. The excitation measurements are used to derive a metallicity gradient for M33 and to quantify the dispersion in the excitation values at a given radius. 52 references.
• Zaritsky, D., Olszewski, E. W., Zaritsky, D., Schommer, R. A., Peterson, R. C., Olszewski, E. W., & Aaronson, M. (1989). Velocities of stars in remote Galactic satellites and the mass of the Galaxy. The Astrophysical Journal, 345(2), 759-769. doi:10.1086/167947
  More info

  Observations of the two most distant known dwarf spheroidal Galactic satellites, Leo I and II, and of two remote globular clusters, Eridanus and Pal 14, are presented. It is demonstrated that etalon spectra can be used for accurate wavelength calibration across the entire observed spectral range. Measured velocities of three stars in Eridanus, two stars in Pal 14, six stars in Leo I, and five stars in Leo II are used to derive that the heliocentric systemic velocities of these systems are - 21 + or - 4, 72 + or - 4, 285 + or - 3, and 70 + or - 4 km/s, respectively. The value of the velocity for Leo I is in significant disagreement with previously published values. Timing arguments are used to estimate that the mass of the Galaxy is at least 13 x 10 to the 11th solar. This value is valid only if Leo I is gravitationally bound to the Galaxy, and arguments supporting this assumption are presented. 70 refs.
• ZARITSKY, D., & WHITE, S. (1988). SIMULATIONS OF SINKING SATELLITES REVISITED. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 235(2), 289-296.
• Zaritsky, D., & White, S. D. (1988). Simulations of sinking satellites revisited. Monthly Notices of the Royal Astronomical Society, 235(1), 289-296. doi:10.1093/mnras/235.1.289
• Scoville, N. Z., Zaritsky, D., Tytler, D., Shaya, E. J., Scoville, N. Z., & Sargent, A. I. (1987). Polarized CCD imaging of the Horsehead Nebula (B33) and Monoceros R2. The Astronomical Journal, 93, 1514. doi:10.1086/114432
  More info

  A technique for large-scale mapping of the magnetic fields in molecular clouds using high-sensitivity CCD images of the light from background stars has been developed. Fractional polarization and its orientation have been mapped in the Horsehead Nebula and Monoceros R2. In each cloud, the magnetic field is aligned with the general magnetic field of the surrounding region, and the percentage polarization does not increase systematically with extinction at visual wavelengths. These results suggest that the dust grains may not be aligned with the magnetic fields in high-density regions. The results also disagree with a previous model for ablation off the surface of the Horsehead Nebula. 31 references.
• Zaritsky, D., & Lo, K. Y. (1986). Evidence for nonaxisymmetric nuclear bulges in spiral galaxies. The Astrophysical Journal, 303, 66. doi:10.1086/164052
• Zaritsky, D., Shaya, E. J., Scoville, N., Sargent, A. I., & Mundy, L. G. (1986). Structure in Dark Clouds as Revealed by Deep CCD Images and IRAS Maps. Bulletin of the American Astronomical Society, 18.
• Zaritsky, D., Tytler, D., Shaya, E. J., Scoville, N., & Sargent, A. I. (1986). Polarized CCD Imaging of the Horsehead Nebula and MonR2. Bulletin of the American Astronomical Society, 18.

Proceedings Publications

• Zaritsky, D., Sivanandam, S., Park, B., Moon, D., Meyer, R. E., Ma, K., Jarvis, M., Henderson, C. R., Grunhut, J., Eisner, J. A., Eikenberry, S. S., Chun, M. Y., Chou, C. Y., & Blank, B. (2018). The wide integral field infrared spectrograph: Commissioning results and on-sky performance. In Ground-based and Airborne Instrumentation for Astronomy VII, 10702.
  More info

  We have recently commissioned a novel infrared (0:9-1:7 μm) integral field spectrograph (IFS) called the Wide Integral Field Infrared Spectrograph (WIFIS). WIFIS is a unique instrument that offers a very large field-of-view (5000 x 2000) on the 2.3-meter Bok telescope at Kitt Peak, USA for seeing-limited observations at moderate spectral resolving power. The measured spatial sampling scale is ~ 1 x 1" and its spectral resolving power is R ~ 2; 500 and 3; 000 in the z J (0:9 - 1:35 μm) and Hshort (1:5 - 1:7 μm) modes, respectively. WIFIS's corresponding etendue is larger than existing near-infrared (NIR) IFSes, which are mostly designed to work with adaptive optics systems and therefore have very narrow fields. For this reason, this instrument is specifically suited for studying very extended objects in the near-infrared such as supernovae remnants, galactic star forming regions, and nearby galaxies, which are not easily accessible by other NIR IFSes. This enables scientific programs that were not originally possible, such as detailed surveys of a large number of nearby galaxies or a full accounting of nucleosynthetic yields of Milky Way supernova remnants. WIFIS is also designed to be easily adaptable to be used with larger telescopes. In this paper, we report on the overall performance characteristics of the instrument, which were measured during our commissioning runs in the second half of 2017. We present measurements of spectral resolving power, image quality, instrumental background, and overall efficiency and sensitivity of WIFIS and compare them with our design expectations. Finally, we present a few example observations that demonstrate WIFIS's full capability to carry out infrared imaging spectroscopy of extended objects, which is enabled by our custom data reduction pipeline.
• Green, R. F., Allen, L., Alvarez Del Castillo, E. M., Brocious, D. K., Corbally, C. J., Davis, D. R., Falco, E. E., Gabor, P., Hall, J. C., Jannuzi, B., Larson, S. M., Mighell, K. J., Nance, C., Shankland, P. D., Walker, C. E., Williams, G., & Zaritsky, D. F. (2014, jan). Progress in Dark Sky Protection in Southern Arizona. In American Astronomical Society Meeting Abstracts, 223, #413.05.
• Meidt, S., Schinnerer, E., Querejeta, M., Ven, G., Zaritsky, D. F., Peletier, R., Knapen, J., Sheth, K., S4G, ., & DAGAL, . (2014, jan). Reconstructing the stellar mass distributions of galaxies using S$_4$G IRAC 3.6 and 4.5 $ mu$m images: the conversion from light to mass. In American Astronomical Society Meeting Abstracts, 223, #453.16.
• O'Brien, G., Sand, D. J., Graham, M. L., Zaritsky, D. F., Pritchet, C., & Hoekstra, H. (2014, jan). Massive Spectroscopic Followup of Transients from the Multi-Epoch Nearby Cluster Survey. In American Astronomical Society Meeting Abstracts, 223, #254.41.
• Olsen, K. A., Nidever, D. L., Gruendl, R. A., Blum, R. D., Walker, A. R., Saha, A., Olszewski, E. W., Munoz, R., Kunder, A. M., Kaleida, C. C., Conn, B., Besla, G., Majewski, S. R., Gallart, C., Monelli, M., Stringfellow, G. S., Zaritsky, D. F., Chu, Y., Van Der Marel, R. P., , Martin, N., et al. (2014, jan). SMASH: The Survey of the MAgellanic Stellar History. In American Astronomical Society Meeting Abstracts, 223, #254.44.
• Sabbi, E., Lennon, D. J., Anderson, J., Van Der Marel, R. P., Aloisi, A., Boyer, M. L., Cignoni, M., De Marchi, G., Mink, S. E., Evans, C. J., Gallagher, J. S., Gordon, K. D., Gouliermis, D., Grebel, E., Koekemoer, A. M., Larsen, S. S., Panagia, N., Ryon, J. E., Smith, L. J., , Tosi, M., et al. (2014, jan). The Hubble Tarantula Treasury Project. In American Astronomical Society Meeting Abstracts, 223, #442.27.
• Graham, M., Sand, D., Bildfell, C., Zaritsky, D. F., & Pritchet, C. (2013, jan). The Multi-Epoch Nearby Cluster Survey: Supernovae and More. In American Astronomical Society Meeting Abstracts, 221, #253.26.
• Zaritsky, D. F., & Team, S. (2013, jan). Using the Lopsidedness of S$_4$G Galaxies to Learn About Disks. In American Astronomical Society Meeting Abstracts, 221, #230.06.
• Finn, R., Earle, A., McCann, A., Rudnick, G., Desai, V., Koopmann, R., Rines, K., Balogh, M., Poggianti, B., Zaritsky, D., Haynes, M., Jablonka, P., & Jablonka, P. (2012, jan). The Local Cluster Survey: Probing Gas Depletion in Nearby Galaxy Groups and Clusters. In American Astronomical Society Meeting Abstracts #219, 219, #338.15.
• Graham, M., Sand, D. J., Bildfell, C., Zaritsky, D., Pritchet, C., & Hoekstra, H. (2012, jan). The Rate of Core Collapse Supernovae in Galaxy Clusters. In American Astronomical Society Meeting Abstracts #219, 219, #108.06.
• Prieto, J. L., Zaritsky, D., Tornambe, A., Raimondo, G., Prieto, J. L., Menci, N., Limongi, M., Harris, J., Giobbi, G., Brocato, E., Badenes, C., & Antonelli, L. A. (2009). Star Formation Around the Youngest Supernova Remnants in the Large Magellanic Cloud: Implications for Type Ia Supernova Progenitors. In AIP Conference Proceedings, 1111, 615-617.
  More info

  We use the star formation history map of the Large Magellanic Cloud recently published by Harris & Zaritsky to study the sites of the four smallest (and presumably youngest) Type Ia supernova remnants: 0509–67.5, 0519–69.0, N103B and DEM L71. We find that three of the four Type Ia remnants are associated with old, metal‐poor stellar populations, with little or no recent star formation. These include SNR 0509–67.5 which is known to have been originated by an extremely bright SN 1991 T‐like event, and yet is located very far away from any star forming regions. It is very unlikely that this bright Type Ia SN had a young stellar progenitor. The fourth Type Ia remnant, SNR N103B is associated with vigorous star formation activity in the last 100 Myr, and might have had a relatively younger and more massive progenitor.
• Zabludoff, A. I., Zaritsky, D., & Zabludoff, A. I. (2008). A merger of subclusters in the galaxy cluster Abell 754. In AIP Conference Proceedings, 336, 216-220.
• Zaritsky, D. (2008). Preliminary evidence for dust in galactic halos. In AIP Conference Proceedings, 336, 165-167.
  More info

  I use B and I photometry of distant galaxies observed through the halos of two nearby spiral galaxies, NGC 2835 and NGC 3521, to test for the existence of dust in galactic halos out to at least a radius of 60 kpc. B−I colors of background galaxies in fields centered along the nearby galaxy’s major axis at a projected separation of 60 kpc are compared to the colors of background galaxies in fields centered at a projected separation of about 220 kpc. Background galaxies in the fields at smaller projected separations have average B−I colors that are 0.067±0.033 mag redder than those in the outer fields. Such a result will occur by chance less than 2.2% of the time and so is taken as preliminary evidence that galaxy halos contain more dust at galactic radii of 60 kpc than 220 kpc.
• Zaritsky, D., Randall, S. W., Markevitch, M., Jones, C., Gonzalez, A. H., Clowe, D., Chung, S., & Bradac, M. (2007). The Bullet Cluster 1E0657-56:. Implications for Dark Matter and Galaxy Evolution. In The Identification of Dark Matter, 128-134.
• Zaritsky, D., Pizagno, J. L., Kobulnicky, H. A., & Kennicutt, R. C. (1999). Chemical constraints on the star formation history in high redshift galaxies. In The 9th astrophysics conference: After the dark ages, when galaxies were young (the Universe at 2, 470, 340-344.
  More info

  It is now possible to study the chemical properties of distant galaxies through emission line diagnostics which have long been used in local H II regions. Initial results from a sample of compact, narrow emission line galaxies at z=0.2 to z=0.5 show a range of metallicities from metal-poor like the SMC to super solar. The oxygen abundances correlate strongly with optical luminosity just like local galaxies. This suggests that the chemical production and retention in individual galaxies is determined predominantly by local characteristics, such as the integrated star formation activity and the depth of the gravitational potential rather than the cosmic star formation history. The ratios of specific elements like nitrogen-to-oxygen can constrain the evolutionary descendants of hi-z galaxies.
• Wittman, D., Tyson, J., Dell'Antonio, I., Becker, A., Margoniner, V., Cohen, J., Norman, D., Loomba, D., Squires, G., Wilson, G., Stubbs, C., Hennawi, J., Spergel, D., Boeshaar, P., Clocchiatti, A., Hamuy, M., Bernstein, G., Gonzalez, A., Guhathakurta, P., , Hu, W., et al. (1993, 2002). The Deep Lens Survey. In SURVEY AND OTHER TELESCOPE TECHNOLOGIES AND DISCOVERIES, 4836, 73-82.

Reviews

• Matheson, T., Garnavich, P., Stanek, K., Bersier, D., Holland, S., Krisciunas, K., Caldwell, N., Berlind, P., Bloom, J., Bolte, M., Bonanos, A., Brown, M., Brown, W., Calkins, M., Challis, P., Chornock, R., Echevarria, L., Eisenstein, D., Everett, M., , Filippenko, A., et al. (2011. Photometry and spectroscopy of GRB 030329 and its associated supernova 2003dh: The first two months(pp 394-407).
• Whitney, B. A., Sewilo, M., Indebetouw, R., Robitaille, T. P., Meixner, M., Gordon, K., Meade, M. R., Babler, B. L., Harris, J., Hora, J. L., Bracker, S., Povich, M. S., Churchwell, E. B., Engelbracht, C. W., For, B., Block, M., Misselt, K., Vijh, U., Leitherer, C., , Kawamura, A., et al. (2007. Spitzer SAGE survey of the Large Magellanic Cloud. III. Star formation and similar to 1000 new candidate Young Stellar Objects(pp 18-43).
• Rudnick, G., von der Linden, A., Pello, R., Aragon-Salamanca, A., Marchesini, D., Clowe, D., De Lucia, G., Halliday, C., Jablonka, P., Milvang-Jensen, B., Poggianti, B., Saglia, R., Simard, L., White, S., & Zaritsky, D. (2006. THE REST-FRAME OPTICAL LUMINOSITY FUNCTION OF CLUSTER GALAXIES AT z < 0.8 AND THE ASSEMBLY OF THE CLUSTER RED SEQUENCE(pp 1559-1588).
• Poggianti, B., Von der Linden, A., De Lucia, G., Desai, ., Simard, L., Halliday, C., Aragon-Salamanca, A., Bower, R., Varela, J., Best, P., Clowe, D., Dalcanton, J., Jablonka, P., Milvang-Jensen, B., Pello, R., Rudnick, G., Saglia, R., White, S., & Zaritsky, D. (1986. The evolution of the star formation activity in galaxies and its dependence on environment(pp 188-215).