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- Rózańska, A., Nikołajuk, M., Czerny, B., Dobrzycki, A., Hryniewicz, K., Bechtold, J., & Ebeling, H. (2014). Absorption features in the quasar HS 1603 + 3820 II. Distance to the absorber obtained from photoionisation modelling. New Astronomy, 28, 70-78.More infoAbstract: We present the photoionisation modelling of the intrinsic absorber in the bright quasar HS 1603 + 3820. We constructed the broad-band spectral energy distribution using the optical/UV/X-ray observations from different instruments as inputs for the photoionisation calculations. The spectra from the Keck telescope show extremely high Civ to Hi ratios, for the first absorber in system A, named A1. This value, together with high column density of Civ ion, place strong constraints on the photoionisation model. We used two photoionisation codes to derive the hydrogen number density at the cloud illuminated surface. By estimating bolometric luminosity of HS 1603 + 3820 using the typical formula for quasars, we calculated the distance to A1. We could find one photoionization solution, by assuming either a constant density cloud (which was modelled using cloudy), or a stratified cloud (which was modelled using titan), as well as the solar abundances. This model explained both the ionic column density of Civ and the high Civ to Hi ratio. The location of A1 is 0.1 pc, and it is situated even closer to the nucleus than the possible location of the Broad Line Region in this object. The upper limit of the distance is sensitive to the adopted covering factor and the carbon abundance. Photoionisation modelling always prefers dense clouds with the number density n0 = 1010 - 1012 cm-3, which explains intrinsic absorption in HS 1603 + 3820. This number density is of the same order as that in the disk atmosphere at the implied distance of A1. Therefore, our results show that the disk wind that escapes from the outermost accretion disk atmosphere can build up dense absorber in quasars. © 2013 Elsevier B.V. All rights reserved.
- Siemiginowska, A., Stawarz, Ł., Cheung, C. C., Aldcroft, T. L., Bechtold, J., Burke, D. J., Evans, D., Holt, J., Jamrozy, M., & Migliori, G. (2012). Deep Chandra X-ray imaging of a nearby radio galaxy 4C+29.30: X-ray/radio connection. Astrophysical Journal, 750(2).More infoAbstract: We report results from our deep Chandra X-ray observations of a nearby radio galaxy, 4C+29.30 (z = 0.0647). The Chandra image resolves structures on sub-arcsec to arcsec scales, revealing complex X-ray morphology and detecting the main radio features: the nucleus, a jet, hotspots, and lobes. The nucleus is absorbed (N H ≃ 3.95 +0.27-0.33 × 10 23cm -2) with an unabsorbed luminosity of L 2-10 keV ≃ (5.08 ± 0.52) × 10 43ergs -1 characteristic of Type 2 active galactic nuclei. Regions of soft (
- Kelly, B. C., Bechtold, J., & Siemiginowska, A. (2011). Erratum: Are the variations in quasar optical flux driven by thermal fluctuations? (Astrophysical Journal (2009) 698 (895)). Astrophysical Journal, 732(2).
- Bian, F., Fan, X., Bechtold, J., McGreer, I. D., Just, D. W., Sand, D. J., Green, R. F., Thompson, D., Peng, C. Y., Seifert, W., Ageorges, N., Juette, M., Knierim, V., & Buschkamp, P. (2010). Lbt/lucifer observations of the z ∼ 2 lensed galaxy J0900+2234. Astrophysical Journal Letters, 725(2), 1877-1885.More infoAbstract: We present rest-frame optical images and spectra of the gravitationally lensed, star-forming galaxy J0900+2234 (z = 2.03). The observations were performed with the newly commissioned LUCIFER1 near-infrared (NIR) instrument mounted on the Large Binocular Telescope. We fitted lens models to the rest-frame optical images and found that the galaxy has an intrinsic effective radius of 7.4 ± 0.8 kpc with a lens magnification factor of about 5 for the A and B components. We also discovered a new arc belonging to another lensed high-z source galaxy, which makes this lens system a potential double Einstein ring system. Using the high signalto-noise ratio rest-frame spectra covered by the H+ K band, we detected Hβ, [O iii], Hα, [N ii], and [S ii] emission lines. Detailed physical properties of this high-z galaxy were derived. The extinction toward the ionized H ii regions (Eg(B -V )) was computed from the flux ratio of Hα and Hβ and appears to be much higher than that toward the stellar continuum (Es (B -V )), derived from the optical and NIR broadband photometry fitting. The metallicity was estimated using N2 and O3N2 indices. It is in the range of 1/5 -1/3 solar abundance, which is much lower than for typical z ∼ 2 star-forming galaxies. From the flux ratio of [S ii]λ6717 and [S ii]λ6732, we found that the electron number density of the H ii regions in the high-z galaxy was ≃1000 cm-3, consistent with other z ∼ 2 galaxies butmuch higher than that in local H ii regions. The star formation rate was estimated via the Hα luminosity, after correction for the lens magnification, to be about 365±69M⊙ yr-1. Combining the FWHM of Hα emission lines and the half-light radius, we found that the dynamical mass of the lensed galaxy is (5.8 ± 0.9) × 1010M ⊙. The gas mass is (5.1 ± 1.1) × 10 10M⊙ from the Hα flux surface density using global Kennicutt-Schmidt law, indicating a very high gas fraction of 0.79 ± 0.19 in J0900+2234. © 2010. The American Astronomical Society. All rights reserved.
- Siemiginowska, A., Burke, D. J., Aldcroft, T. L., Worrall, D. M., Allen, S., Bechtold, J., Clarke, T., & Cheung, C. C. (2010). High-redshift X-ray cooling-core cluster associated with the luminous radio-loud quasar 3C 186. Astrophysical Journal Letters, 722(1), 102-111.More infoAbstract: We present the first results from a new, deep (200 ks) Chandra observation of the X-ray luminous galaxy cluster surrounding the powerful (L ∼ 10 47 erg s-1), high-redshift (z = 1.067), compact-steep-spectrum radio-loud quasar 3C 186. The diffuse X-ray emission from the cluster has a roughly ellipsoidal shape and extends out to radii of at least ∼60 arcsec (∼500 kpc). The centroid of the diffuse X-ray emission is offset by 0.68±0″ .11 (∼5.5±0.9 kpc) from the position of the quasar. We measure a cluster mass within the radius at which the mean enclosed density is 2500 times the critical density, r2500 = 283+18-13 kpc, of 1.02+0.21-0.14 ×1014M⊙. The gas-mass fraction within this radius is fgas = 0.129+0.015-0.016. This value is consistent with measurements at lower redshifts and implies minimal evolution in the fgas(z) relation for hot, massive clusters at 0 < z < 1.1. The measured metal abundance of 0.42+0.08-0.07 Solar is consistent with the abundance observed in other massive, high-redshift clusters. The spatially resolved temperature profile for the cluster shows a drop in temperature, from kT ∼ 8 keV to kT ∼ 3 keV, in its central regions that is characteristic of cooling-core clusters. This is the first spectroscopic identification of a cooling-core cluster atz > 1. We measure cooling times for the X-ray emitting gas at radii of 50 kpc and 25 kpc of 1.7 ± 0.2 × 109 years and 7.5±2.6×10 8 years, as well as a nominal cooling rate (in the absence of heating) of 400±190M⊙ year-1 within the central 100 kpc. In principle, the cooling gas can supply enough fuel to support the growth of the supermassive black hole and to power the luminous quasar. The radiative power of the quasar exceeds by a factor of 10 the kinematic power of the central radio source, suggesting that radiative heating may be important at intermittent intervals in cluster cores. 2010. The American Astronomical Society. All rights reserved.
- Kelly, B. C., Bechtold, J., & Siemiginowska, A. (2009). Are the variations in quasar optical flux driven by thermal fluctuations?. Astrophysical Journal Letters, 698(1), 895-910.More infoAbstract: We analyze a sample of optical light curves for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z < 2.8, 1042 ≲ λL λ(5100 ) ≲ 10 46, and 106 ≲ M BH/M ⊙ ≲ 1010. We model the light curves as a continuous time stochastic process, providing a natural means of estimating the characteristic timescale and amplitude of quasar variations. We employ a Bayesian approach to estimate the characteristic timescale and amplitude of flux variations; our approach is not affected by biases introduced from discrete sampling effects. We find that the characteristic timescales strongly correlate with black hole mass and luminosity, and are consistent with disk orbital or thermal timescales. In addition, the amplitude of short-timescale variations is significantly anticorrelated with black hole mass and luminosity. We interpret the optical flux fluctuations as resulting from thermal fluctuations that are driven by an underlying stochastic process, such as a turbulent magnetic field. In addition, the intranight variations in optical flux implied by our empirical model are ≲0.02 mag, consistent with current microvariability observations of radio-quiet quasars. Our stochastic model is therefore able to unify both long- and short-timescale optical variations in radio-quiet quasars as resulting from the same underlying process, while radio-loud quasars have an additional variability component that operates on timescales ≲1 day. © 2009. The American Astronomical Society. All rights reserved..
- McLeod, K. K., & Bechtold, J. (2009). Host galaxies of z = 4 quasars. Astrophysical Journal Letters, 704(1), 415-438.More infoAbstract: We have undertaken a project to investigate the host galaxies and environments of a sample of quasars at z 4. In this paper, we describe deep near-infrared imaging of 34 targets using the Magellan I and Gemini North telescopes. We discuss in detail special challenges of distortion and nonlinearity that must be addressed when performing point-spread function (PSF) subtraction with data from these telescopes and their IR cameras, especially in very good seeing. We derive black hole masses from emission-line spectroscopy, and we calculate accretion rates from our Ks -band photometry, which directly samples the rest frame B for these objects. We introduce a new isophotal diameter technique for estimating host galaxy luminosities. We report the detection of four host galaxies on our deepest, sharpest images, and present upper limits for the others. We find that if host galaxies passively evolve such that they brighten by 2 mag or more in the rest-frame B band between the present and z = 4, then high-z hosts are less massive at a given black hole mass than are their low-z counterparts. We argue that the most massive hosts plateau at ≲10 L*. We estimate the importance of selection effects on this survey and the subsequent limitations of our conclusions. These results are in broad agreement with recent semianalytical models for the formation of luminous quasars and their host spheroids by mergers of gas-rich galaxies, with significant dissipation, and self-regulation of black hole growth and star formation by the burst of merger-induced quasar activity. © 2009 The American Astronomical Society. All rights reserved.
- Schwope, A. D., Erben, T., Kohnert, J., Lamer, G., Steinmetz, M., Strassmeier, K., Zinnecker, H., Bechtold, J., Diolaiti, E., Fontana, A., Gallozzi, S., Giallongo, E., Ragazzoni, R., Santis, C. D., & Testa, V. (2009). The isolated neutron star RBS1774 revisited. Astronomy and Astrophysics, 499(1), 267-272.More infoAbstract: We report optical B-band observations with the Large Binocular Telescope (LBT) of the isolated neutron star RBS1774. The stacked image with a total exposure of 2.h5 reveals a candidate optical counterpart at m B = 26.96 0.20 at position α(2000) = 21h43m03.s40, δ(2000) = +06°5417.5, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and derive revised spectral and positional parameters. The predicted optical flux from the extrapolated X-ray spectrum is likely twice as high as reported before. The measured optical flux exceeds the extrapolated X-ray spectral flux by a factor ̃ 40 (15-60 at 1σ confidence). We interpret our detection and the spectral energy distribution as further evidence of a temperature structure over the neutron star's surface and present a pure thermal model reflecting both the SED and the pulsed fraction of the light curve. © 2009 ESO.
- Dai, X., Garnavich, P. M., Prieto, J. L., Stanek, K. Z., Kochanek, C. S., Bechtold, J., Bouche, N., Buschkamp, P., Diolaiti, E., Fan, X., Giallongo, E., Gredel, R., Hill, J. M., Jiang, L., McClelland, C., Milne, P., Pedichini, F., Pogge, R. W., Ragazzoni, R., , Rhoads, J., et al. (2008). Go long, go deep: finding optical jet breaks for SWIFT-ERA GRBs with the lbt. Astrophysical Journal, 682(2 PART 2), L77-L80.More infoAbstract: Using the 8.4 m Large Binocular Telescope, we observed six GRB afterglows from 2.8 hr to 30.8 days after the burst triggers to systematically probe the late-time behaviors of afterglows including jet breaks, flares, and supernova bumps. We detected five afterglows with Sloan r′ magnitudes ranging from 23.0 to 26.3 mag. The depth of our observations allows us to extend the temporal baseline for measuring jet breaks by another decade in timescale. We detected two jet breaks and a third candidate, all of which are not detectable without deep, latetime optical observations. In the other three cases, we do not detect the jet breaks either because of contamination from the host galaxy light, the presence of a supernova bump, or the intrinsic faintness of the optical afterglow. This suggests that the basic picture that GRBs are collimated is still valid and that the apparent lack of Swift jet breaks is due to poorly sampled afterglow light curves, particularly at late times. © 2008. The American Astronomical Society.
- Kelly, B. C., Bechtold, J., Trump, J. R., Vestergaard, M., & Siemiginowska, M. (2008). Observational constraints on the dependence of radio-quiet quasar X-ray emission on black hole mass and accretion rate. Astrophysical Journal, Supplement Series, 176(2), 355-373.More infoAbstract: In this work we use a sample of 318 radio-quiet quasars (RQQs) to investigate the dependence of the ratio of optical/UV flux to X-ray flux, αox, and the X-ray photon index, ΓX , on black hole mass, UV relative to Eddington luminosity, and X-ray relative to Eddington luminosity. Our sample is drawn from the literature, with X-ray data from ROSAT and Chandra, and optical data mostly from the SDSS; 153 of these sources have estimates of ΓX from Chandra. We estimate MBH using standard estimates derived from the HβMg II, and C IV broad emission lines. Our sample spans a broad range in black hole mass (106 ≲ M BH/M⊙ ≲ 1010), redshift (0 < z < 4.8), and luminosity (1043 ≲ λLλ (2500 Å)[ergs s-1] ≲ 1048). We find that αox increases with increasing MBH and L UV/LEdd and decreases with increasing LX/L Edd. In addition, we confirm the correlation seen in previous studies between ΓX and MBH and both LUV/L Edd and LX/LEdd; however, we also find evidence that the dependence of ΓX of these quantities is not monotonic, changing sign at MBH ∼ 3 × 108 M ⊙. We argue that the αox correlations imply that the fraction of bolometric luminosity emitted by the accretion disk, as compared to the corona, increases with increasing accretion rate relative to the Eddington rate, ṁ. In addition, we argue that the ΓX trends are caused by a dependence of X-ray spectral index on ṁ. We discuss our results within the context of accretion models with Comptonizing corona and discuss the implications of the αox correlations for quasar feedback. To date, this is the largest study of the dependence of RQQ X-ray parameters on black hole mass and related quantities, and the first to attempt to correct for the large statistical uncertainty in the broad-line mass estimates. © 2008. The American Astronomical Society. All rights reserved.
- Martin, N. F., Coleman, M. G., T., J., Rix, H., Bell, E. F., Sand, D. J., Hill, J. M., Thompson, D., Burwitz, V., Giallongo, E., Ragazzoni, R., Diolaiti, E., Gasparo, F., Grazian, A., Pedichini, F., & Bechtold, J. (2008). A deep large binocular telescope view of the Canes Venatici I dwarf galaxy. Astrophysical Journal, 672(1 PART 2), L13-L16.More infoAbstract: We present the first deep color-magnitude diagram of the Canes Venatici I (CVn I) dwarf galaxy from observations with the wide-field Large Binocular Camera on the Large Binocular Telescope. Reaching down to the main-sequence turnoff of the oldest stars, it reveals a dichotomy in the stellar populations of CVn I: it harbors an old (≳ 10 Gyr), metal-poor ([Fe/H]∼-2.0), and spatially extended population along with a much younger (∼1.4-2.0 Gyr), 0.5 dex more metal-rich, and spatially more concentrated population. These young stars are also offset by 64+40-20 pc to the east of the galaxy center. The data suggest that this young population, which represents ∼3%-5% of the stellar mass of the galaxy within its half-light radius, should be identified with the kinematically cold stellar component found in a recent spectroscopic survey. CVn I therefore follows the behavior of the other remote MW dwarf spheroidals, which all contain intermediate-age and/or young populations: a complex star formation history is possible in extremely low mass galaxies. © 2008. The American Astronomical Society, All rights reserved.
- Pasquali, A., Leroy, A., Rix, H. -., Walter, F., Herbst, T., Giallongo, E., Ragazzoni, R., Baruffolo, A., Speziali, R., Hill, J., Beccari, G., Bouché, N., Buschkamp, P., Kochanek, C., Skillman, E., & Bechtold, J. (2008). The large binocular telescope panoramic view of the recent star formation activity in IC 2574. Astrophysical Journal, 687(2), 1004-1018.More infoAbstract: We present deep imaging of the star-forming dwarf galaxy IC 2574 in the M81 group taken with the Large Binocular Telescope (LET) in order to study in detail the recent star formation history of this galaxy and to constrain the stellar feedback on its H I gas. We identify the star-forming areas in the galaxy by removing a smooth disk component from the optical images. We construct pixel-by-pixel maps of stellar age and stellar mass surface density in these regions by comparing their observed colors with simple stellar populations synthesized with Starburst99. We find that an older burst occurred about 100 Myr ago within the inner 4 kpc and that a younger burst happened in the last 10 Myr mostly at galactocentric radii between 4 and 8 kpc. We analyze the stellar populations residing in the known H I holes of IC 2574. Our results indicate that, even at the remarkable photometric depth of the LBT data, there is no clear one-to-one association between the observed H I holes and the most recent bursts of star formation in IC 2574. The stellar populations formed during the younger burst are usually located at the periphery of the H I holes and are seen to be younger than the holes' dynamical age. The kinetic energy of hole expansion is found to be, on average, 10% of the total stellar energy released by the stellar winds and supernova explosions of the young stellar populations within the holes. With the help of control apertures distributed across the galaxy we estimate that the kinetic energy stored in the H I gas in the form of its local velocity dispersion is about 35% of the total stellar energy.
- Prieto, J. L., Kistler, M. D., Thompson, T. A., Yüksel, H., Kochanek, C. S., Stanek, K. Z., Beacom, J. F., Martini, P., Pasquali, A., & Bechtold, J. (2008). Discovery of the dust-enshrouded PROGENITOR of SN 2008S with SPITZER. Astrophysical Journal, 681(1 PART 2), L9-L12.More infoAbstract: We report the discovery of the progenitor of the recent Type IIn SN 2008S in the nearby galaxy NGC 6946. Surprisingly, it was not found in deep, preexplosion optical images of its host galaxy taken with the Large Binocular Telescope, but only through examination of archival Spitzer mid-IR data. A source coincident with the SN 2008S position is clearly detected in the 4.5, 5.8, and 8.0 μm IRAC bands, showing no evident variability in the 3 years prior to the explosion, yet is undetected at 3.6 and 24 μm. The distinct presence of ~440 K dust, along with stringent LBT limits on the optical fluxes, suggests that the progenitor of SN 2008S was engulfed in a shroud of its own dust. The inferred luminosity of ≈3.5 × 104 L⊙ implies a modest mass of ~10 M⊙. We conclude that objects like SN 2008S are not exclusively associated with the deaths or outbursts of very massive η Carinae-like objects. This conclusion holds based solely on the optical flux limits even if our identification of the progenitor with the mid-IR source is incorrect. © 2008, The American Astronomical Society, All rights reserved.
- Prieto, J. L., Stanek, K. Z., Kochanek, C. S., Weisz, D. R., Baruffolo, A., Bechtold, J., Burwitz, V., Santis, C. D., Gallozzi, S., Garnavich, P. M., Giallongo, E., Hill, J. M., Pogge, R. W., Ragazzoni, R., Speziali, R., Thompson, D. J., & Wagner, R. M. (2008). Lbt discovery of a yellow supergiant eclipsing binary in the dwarf galaxy holmberg IX. Astrophysical Journal, 673(1 PART 2), L59-L62.More infoAbstract: In a variability survey of M81 using the Large Binocular Telescope we have discovered a peculiar eclipsing binary (Mv ∼ -7.1) in the field of the dwarf galaxy Holmberg IX. It has a period of 271 days, and the light curve is well fit by an overcontact model in which both stars are overflowing their Roche lobes. It is composed of two yellow supergiants (V -I ≃ 1 mag, Teff ≃ 4800 K), rather than the far more common red or blue supergiants. Such systems must be rare. While we failed to find any similar systems in the literature, we did, however, note a second example. The SMC F0 supergiant R47 is a bright (Mv ∼ -7.5) periodic variable whose All Sky Automated Survey (ASAS) light curve is well fit as a contact binary with a 181 day period. We propose that these systems are the progenitors of supernovae like SN 2004et and SN 2006ov, which appeared to have yellow progenitors. The binary interactions (mass transfer, mass loss) limit the size of the supergiant to give it a higher surface temperature than an isolated star at the same core evolutionary stage. We also discuss the possibility of this variable being a long-period Cepheid. © 2008. The American Astronomical Society.
- Coleman, M. G., T.A., J., Martin, N. F., Rix, H., Sand, D. J., Bell, E. F., Pogge, R. W., Thompson, D. J., Hippelein, H., Giallongo, E., Ragazzoni, R., DiPaola, A., Farinato, J., Smareglia, R., Testa, V., Bechtold, J., Hill, J. M., Garnavich, P. M., & Green, R. F. (2007). The elongated structure of the Hercules dwarf spheroidal galaxy from deep Large Binocular Telescope imaging. Astrophysical Journal, 668(1 PART 2), L43-L46.More infoAbstract: We present a deep, wide-field photometric survey of the newly discovered Hercules dwarf spheroidal galaxy (dSph), based on data from the Large Binocular Telescope. Images in B, V, and r were obtained with the Large Binocular Camera covering a 23′ × 23′ field of view to a magnitude of ∼25.5 (5 σ;). This permitted the construction of color-magnitude diagrams that reach approximately 1.5 mag below the Hercules main-sequence turnoff. Three-filter photometry allowed us to preferentially select probable Hercules member stars and to examine the structure of this system at a previously unattained level. We find that the Hercules dwarf is highly elongated (3: 1) considerably more so than any other dSph satellite of the Milky Way, except the disrupting Sagittarius dwarf. Although we cannot rule out that the unusual structure is intrinsic to Hercules as an equilibrium system, our results suggest tidal disruption as a likely cause of this highly elliptical structure. Given the relatively large galactocentric distance of this system (± 12 kpc), signs of tidal disruption would require the Hercules dwarf to be on a highly eccentric orbit around the Milky Way. © 2007, The American Astronomical Society.
- Dobrzycki, A., Nikolajuk, M., Bechtold, J., Ebeling, H., Czerny, B., & Rózańska, A. (2007). Absorption spectrum of the quasar HS1603+3820. Astronomy and Astrophysics, 476(3), 1205-1217.More infoAbstract: Context.We present multi-wavelength observations of the bright quasar HS1603+3820: the optical data taken with the MMT and Keck telescopes, with the 40-50 km-1 resolution, and X-ray data taken by the Chandra X-ray Observatory satellite.Aims.The optical spectra contain a very large number of absorption lines from numerous heavy elements. Our goal is to analyze these features to obtain constraints on the properties of associated absorbers, to be used in modeling of the quasar intrinsic flux and properties of the clouds.Methods.We have determined the properties - column densities and redshifts - of the individual components. We derived the X-ray properties of HS1603+3820 and the optical-to-X-ray slope index .Results.We found alpha;ox of 1.70, which is at the high end of the typical range for a radio quiet quasar. We found 49 individual heavy element absorption clouds, which can be grouped into eleven distinct systems. Absorbers from the associated system, which likely is the one spatially closest to the quasar, show large CIV to HI column density ratio, reaching ∼20.Conclusions.Intrinsic X-ray properties of the quasar are typical. Determination of column densities of ions (including hydrogen) gives a strong foundation for modeling of the quasar ionising flux. © 2007 ESO.
- Kelly, B. C., & Bechtold, J. (2007). Virial masses of black holes from single epoch spectra of active galactic nuclei. Astrophysical Journal, Supplement Series, 168(1), 1-18.More infoAbstract: We describe the general problem of estimating black hole masses of active galactic nuclei (AGNs) by calculating the conditional probability distribution of MBH given some set of observables. Special attention is given to the case where one uses the AGN continuum luminosity and emission line widths to estimate MBH, and we outline how to set up the conditional probability distribution of MBH given the observed luminosity, line width, and redshift. We show how to combine the broad-line estimates of M BH with information from an intrinsic correlation between M BH and L, and from the intrinsic distribution of MBH, in a manner that improves the estimates of MBH. Simulation was used to assess how the distribution of MBH inferred from the broad-line mass estimates differs from the intrinsic distribution, and we find that this can lead to an inferred distribution that is too broad. We use these results and a sample of 25 sources that have recent reverberation mapping estimates of AGN black hole masses to investigate the effectiveness of using the C IV emission line to estimate MBH and to indirectly probe the C IV region size-luminosity (R-L) relationship. A linear regression of log L λ (1549 Å) on log MBH found that L 1549 ∝ MBH1.17±0.22. A linear regression also found that MBH ∝ L15490.41±0.07FWHMC IV2, implying a C IV R-L relationship of the form RC IV ∝ L15490.41±0.07. Including the C IV line FWHM resulted in a reduction of a factor of ∼ 1/3 in the error in the estimates of M BH over simply using the continuum luminosity, statistically justifying its use. We estimated MBH from both C IV and Hβ for a sample of 100 sources, including new spectra of 29 quasars. We find that the two emission lines give consistent estimates if one assumes R ∝ L UV1/2 for both lines. © 2007. The American Astronomical Society. All rights reserved.
- Kelly, B. C., Bechtold, J., Siemiginowska, A., Aldcroft, T., & Sobolewska, M. (2007). Evolution of the X-ray emission of radio-quiet quasars. Astrophysical Journal, 657(1 I), 116-134.More infoAbstract: We report new Chandra observations of seven optically faint, z ∼ 4 radio-quiet quasars (RQQs). We have combined these new observations with previous Chandra observations of RQQs to create a sample of 174 sources. These sources have 0.1 < z < 4.7, and 1044 ergs s-1 < νLν (2500 Å) < 1048 ergs s-1. The X-ray detection fraction is 90%. We find that the X-ray loudness of RQQs decreases with UV luminosity and increases with redshift. The model that is best supported by the data has a linear dependence of optical to X-ray ratio αox on cosmic time and a quadratic dependence of αox on log LUV, where αox becomes X-ray quiet more rapidly at higher log LUV. We find no significant evidence for a relationship between the X-ray photon index Fx and the UV luminosity, and we find marginally significant evidence that the X-ray continuum flattens with increasing z (2 σ). The Τx-z anticorrelation may be the result of X-ray spectral curvature, redshifting of a Compton reflection component into the observed Chandra band, and/or redshifting of a soft excess out of the observed Chandra band. Using the results for Τx, we show that the αox-z relationship is unlikely to be a spurious result caused by redshifting of the observable X-ray spectral region. A correlation between αox and z implies evolution of the accretion process. We present a qualitative comparison of these new results with models for accretion disk emission. © 2007, The American Astronomical Society. All rights reserved.
- Siemiginowska, A., Stawarz, Ł., Cheung, C. C., Harris, D. E., Sikora, M., Aldcroft, T. L., & Bechtold, J. (2007). The 300 kpc long X-ray jet in PKS 1127-145, z = 1.18 quasar: Constraining X-ray emission models. Astrophysical Journal, 657(1 I), 145-158.More infoAbstract: We present a ∼100 ks Chandra X-ray observation and new VLA radio data of the large-scale, 300 kpc long X-ray jet in PKS 1127-145, a radio-loud quasar at redshiftz = 1.18. With this deep X-ray observation we now clearly discern the complex X-ray jet morphology and see substructure within the knots. The X-ray and radio jet intensity profiles are seen to be strikingly different, with the radio emission peaking strongly at the two outer knots while the X-ray emission is strongest in the inner jet region. The jet X-ray surface brightness gradually decreases by an order of magnitude going out from the core. The new X-ray data contain sufficient counts for spectral analysis of the key jet features. The X-ray energy index of the inner jet is relatively flat with αX = 0.66 ± 0.15 and steep in the outer jet with αX = 1.0 ± 0.2. We discuss the constraints implied by the new data on the X-ray emission models and conclude that "one-zone" models fail and that at least a two-component model is needed to explain the jet's broadband emission. We propose that the X-ray emission originates in the jet proper while the bulk of the radio emission comes from a surrounding jet sheath. We also consider intermittent jet activity as a possible cause of the observed jet morphology. © 2007. The American Astronomical Society, All rights reserved.
- Meiring, J. D., Kulkarni, V. P., Khare, P., Bechtold, J., York, D. G., Cui, J., Lauroesch, J. T., P., A., & Nakamura, O. (2006). Elemental abundance measurements in low-redshift damped Lyman α absorbers. Monthly Notices of the Royal Astronomical Society, 370(1), 43-62.More infoAbstract: We present elemental abundance measurements for nine damped Lyman α (Lyα) systems (DLAs) and one sub-DLA at 0.1 ≤ z ≤ 1.5 from recent observations with the Multiple Mirror Telescope (MMT). Most of these absorbers are found to be metal poor, while two are found to have ≈30-50 per cent solar metallicities. Combining our data with other data from the literature, we find that the systems with higher [Zn/H] also have stronger depletion as measured by [Cr/Zn] and [Fe/Zn]. The relationship between the metallicity and Hi column density is also investigated. Together with our previous MMT survey, we have discovered two of the four known absorbers at z < 1.5 that lie above (although near) the 'obscuration threshold'. This appears to be a result of selecting absorbers with strong metal lines in our sample. It would be interesting to find other similar systems by observing a larger sample and study how much such systems contribute to the cosmic budget of metals. Finally, an analysis of the N HI-weighted mean metallicity versus redshift for our sample combined with data from the literature supports previous conclusions that the N HI-weighted mean global DLA metallicity rises slowly at best and falls short of solar levels by a factor of >4 even at z = 0. © 2006 RAS.
- Siemiginowska, A., Cheung, C. C., Massa, S. L., Burke, D., Aldcroft, T. L., Bechtold, J., Elvis, M., & Worrall, D. M. (2006). AGN feedback and evolution of radio sources: Discovery of an x-ray cluster associated with Z=1 quasar. European Space Agency, (Special Publication) ESA SP, 2(604), 705-709.More infoAbstract: We report the first significant detection of an X-ray cluster associated with a powerful (Lbol ∼ 1047 erg sec-1) radio-loud quasar at high redshift (z=1.06). Diffuse X-ray emission is detected out to ∼ 120 kpc from the CSS quasar 3C 186. A strong Fe-line emission at the Zrest = 1.06 confirms its thermal nature. We find that the CSS radio source is highly overpressured with respect to the thermal cluster medium by 2-3 orders of magnitude. This provides direct observational evidence that the radio source is not thermally confined as posited in the "frustrated" scenario for CSS sources. Instead, the radio source may be young and at an early stage of its evolution. This source provides the first detection of the AGN in outburst in the center of a cooling flow cluster. Powerful radio sources are thought to be triggered by the cooling flows. The evidence for the AGN activity and intermittent outbursts comes from the X-ray morphology of low redshift clusters, which usually do not harbour quasars. 3C186 is a young active radio source which can supply the energy into the cluster and potentially prevent its cooling. We discuss energetics related to the quasar activity and the cluster cooling flow, and possible feedback between the evolving radio source and the cluster.
- Chun, L. y., S., D., & Bechtold, J. (2005). The discovery of extended thermal X-ray emission from PKS 2152-699: Evidence for a "jet-cloud" interaction. Astrophysical Journal Letters, 618(2 I), 609-617.More infoAbstract: A Chandra ACIS-S observation of PKS 2152-699 reveals thermal emission from a diffuse region around the core and a hotspot located 10″ northeast from the core. This is the first detection of thermal X-ray radiation on kiloparsec scales from an extragalactic radio source. Two other hotspots located 47″ north-northeast and 26″ southwest from the core were also detected. Using a Raymond-Smith model, the first hotspot can be characterized with a thermal plasma temperature of 2.6 × 106 K and an electron number density of 0.17 cm-3. These values correspond to a cooling time of ∼1.6 × 107 yr. In addition, an emission line from the hotspot, possibly Fe xxv, was detected at rest wavelength 10.04 Å. The thermal X-ray emission from the first hotspot is offset from the radio emission but is coincident with optical filaments detected with broadband filters of Hubble Space Telescope WFPC2. The best explanation for the X-ray, radio, and optical emission is that of a "jet-cloud" interaction. The diffuse emission around the nucleus of PKS 2152-699 can be modeled as a thermal plasma with a temperature of 1.2 × 107 K and a luminosity of 1.8 × 1041 ergs s-1. This emission appears to be asymmetric, with a small extension toward hotspot A, similar to a jet. An optical hotspot (extended emission-line region) is seen less than 1″ away from this extension in the direction of the core. This indicates that the extension may be caused by the jet interacting with an inner interstellar medium cloud, or that it is due to entrainment of hot gas. Future observations are discussed.
- Cui, J., Bechtold, J., Jian, G. E., & Meyer, D. M. (2005). Molecular hydrogen in the damped Lyα absorber of Q1331+170. Astrophysical Journal Letters, 633(2 I), 649-663.More infoAbstract: We used HST STIS to obtain the spectrum of molecular hydrogen associated with the damped Lyα system at zabs = 1.7765 toward the quasar Q1331+170 at zem = 2.084. Strong H2 absorption was detected, with a total H2 column density of N(H2) = (4.45 ± 0.36) × 1019 cm-2. The molecular hydrogen traction is fH2 = 2NH2/(NH I, + 2N H2) = 5.6% ± 0.7%, which is the greatest value reported so far in any redshifted damped Lyα system. This results from the combined effect of a relatively high dust-to-gas ratio, a low gas temperature, and an extremely low ambient UV radiation field. Based on the observed population of J states, we estimate the photoabsorption rate to be Rabs = (7-6 ±2.4) × 10-13 s-1, corresponding to a local UV radiation field of J(1000 Å) ≈ 2.1 × 10-3 J 1000 Å⊙, where J1000 Å, ⊙is the UV intensity at 1000 Å in the solar neighborhood. This is comparable to the metagalactic UV background intensity at this redshift and implies an extremely low star formation rate in the absorber's environment. We construct a simple model to describe the structure of the H2 absorber, with a best-fit total hydrogen number density of n(H) ≈ 0.2 cm-3 and an electron temperature of Te ≈ 140 K. Assuming spherical symmetry, the mass of the H2 cloud is estimated to be ≈ 6.5 × 107 M⊙, larger than the masses of most giant molecular clouds in the Milky Way and nearby galaxies. The extinction of Q1331+170 due to the intervening DLA is EB-V ≈ 0.037, and we also find that the extinction by DLAs with firm H2 detections is significantly greater than those for which only upper limits of fH2 have been determined. The observed CO-to-H2 column density ratio is NCO/H H2 < 2.5 × 10-7, which is similar to the value measured for diffuse molecular clouds in the Galactic ISM. Finally, applying the inferred physical conditions to the observed C I fine structure excitation, we estimate the cosmic microwave background temperature to be TCMB = (7.2 ± 0.8) K at z = 1.77654, consistent with the predicted value of 7.566 K from the standard cosmology. © 2005. The American Astronomical Society. All rights reserved.
- Siemiginowska, A., Cheung, C. C., Lamassa, S., Burke, D. J., Aldcroft, T. L., Bechtold, J., Elvis, M., & Worrall, D. M. (2005). X-ray cluster associated with the z = 1.063 CSS quasar 3C 186: The jet is not frustrated. Astrophysical Journal Letters, 632(1 I), 110-121.More infoAbstract: We report the Chandra discovery of an X-ray cluster at redshift z = 1.063 associated with the compact steep spectrum (CSS) radio-loud quasar 3C 186 (Q0740+380). Diffuse X-ray emission is detected out to ∼120 kpc from the quasar and contains 741 ±40 net counts. The X-ray spectrum of the extended emission shows strong Fe-line emission (EW = 412 eV) at the quasar redshift and confirms the thermal nature of this diffuse component. We measure a cluster temperature of 5.2-0.9+1.2 keV and an X-ray luminosity LX(0.5-2 keV) ∼ 6 × 1044 ergs s -1, which are in agreement with the luminosity-temperature relation for high-redshift clusters. This is the first detection of a bright X-ray cluster around a luminous (Lbol ∼ 1047 ergs s -1) CSS quasar at high redshift and is only the fifth z > 1 X-ray cluster detected. We find that the CSS radio source is highly overpressured with respect to the thermal cluster medium by about 3 orders of magnitude. This provides direct observational evidence that the radio source is not thermally confined as posited in the "frustrated" scenario for CSS sources. Instead, it appears that the radio source may be young and we are observing it at an early stage of its evolution. In that case the radio source could supply the energy into the cluster and potentially prevent its cooling. © 2005. The American Astronomical Society. All rights reserved.
- Błazejowski, M., Siemiginowska, A., Sikora, M., Moderski, R., & Bechtold, J. (2004). X-ray emission from the quasar PKS 1127-145: Comptonized infrared photons on parsec scales. Astrophysical Journal Letters, 600(1 II), L27-L30.More infoAbstract: We model the broadband spectral energy distribution of the innermost "core-jet" region of the redshift z = 1.187 quasar PKS 1127-145. We propose a scenario in which the high-energy photons are produced via the Compton scattering of thermal IR radiation by the relativistic particles in a parsec-scale jet. The high-energy spectrum, together with the observed radio variability and superluminal expansion, suggest that PKS 1127-145 may be a blazar, despite the fact that its optical/UV component is likely dominated by thermal radiation from an accretion disk. The relation of PKS 1127-145 to MeV blazars is discussed.
- Bechtold, J., Siemiginowska, A., Shields, J., Czerny, B., Janiuk, A., Hamann, F., Aldcroft, T. L., Elvis, M., & Dobrzycki, A. (2003). Chandra survey of radio-quiet, high-redshift quasars. Astrophysical Journal Letters, 588(1 I), 119-127.More infoAbstract: We observed 17 optically selected, radio-quiet, high-redshift quasars with the Chandra ACIS and detected 16 of them. The quasars have redshifts between 3.70 and 6.28 and include the highest-redshift quasars known. When compared with low-redshift quasars observed with ROSAT, these high-redshift quasars are significantly more X-ray-quiet. We also find that the X-ray spectral index of the high-redshift objects is flatter than the average at lower redshift. These trends confirm the predictions of models in which the accretion flow is described by a cold, optically thick accretion disk surrounded by a hot, optically thin corona, provided the viscosity parameter α ≥ 0.02. The high-redshift quasars have supermassive black holes, with masses of ∼10 10 M⊙, and are accreting material at ∼0.1 times the Eddington limit. We detect 10 X-ray photons from the z = 6.28 quasar SDSS 1030+0524, which might have a Gunn-Peterson trough and be near the redshift of reionization of the intergalactic medium. The X-ray data place an upper limit on the optical depth of the intergalactic medium, τ(IGM) < 10 6, compared to the lower limit from the spectrum of Lyα and Lyβ, which implies τ(IGM) > 20.
- Reynolds, R. O., Jian, G. e., Lloyd-Hart, M., & Bechtold, J. (2003). Adaptive optics echelle spectrograph for radial velocity studies. Proceedings of SPIE - The International Society for Optical Engineering, 5170, 283-291.More infoAbstract: Radial velocity studies represent the most successful method to date for the detection of extrasolar planets. Although radial velocity (v r) measurement precision of 3 m s -1 is routinely achieved in some programs, it is important to understand and minimize sources of experimental error. Furthermore, velocity variations resulting from astrophysical processes contribute to velocity errors, and must be removed if precision is to be further improved. The use of spectrographs with telescopes having high order adaptive optics (AO) systems offers the possibility of achieving near diffraction-limited very high spectral resolution at visible wavelengths on ground-based telescopes. The small stellar image diameters obtained with adaptively corrected systems allow high resolution without a large loss of light at the spectrograph entrance aperture. The Adaptively Corrected Echelle Spectrograph (ACES), designed at Steward Observatory for a spectral resolution R - 200,000, couples the telescope image to the instrument with an 8-10μm diameter near single-mode optical fiber. The shorter effective slit permits the placement of more echelle orders on the detector after cross dispersion, with a correspondingly greater wavelength coverage per exposure. This simultaneous high resolution and large wavelength coverage can be used to improve the precision of radial velocity studies by improving wavelength calibration, reducing dataset internal errors, and permitting better characterization and removal of effects intrinsic to the stars themselves.
- Siemiginowska, A., Aldcroft, T. L., Bechtold, J., Brunetti, G., Elvis, M., & Stanghellini, C. (2003). X-ray emission from gigahertz peaked/compact steep spectrum sources. Publications of the Astronomical Society of Australia, 20(1), 113-117.More infoAbstract: The high spatial resolution of the Chandra X-ray Observatory allows us to study the environment of GPS/CSS sources to within an arcsec of the strong compact core. We present the discovery of X-ray jets in two GPS quasars, PKS1127-145 and B2 0738+313, indicating that X-ray emission associated with the relativistic plasma is present at large distances from the GPS nucleus. We also discuss first results from Chandra observations of our GPS/CSS sample. We find that six out of ten sources show intrinsic absorption at a level which may be sufficient to confine the GPS source. © Astronomical Society of Australia 2003.
- Siemiginowska, A., Stanghellini, C., Brunetti, G., Aldcroft, T. L., Bechtold, J., Elvis, M., & Harris, D. E. (2003). Discovery of X-ray jets in GPS sources. New Astronomy Reviews, 47(6-7), 467-469.More infoAbstract: Giga-Hertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources have compact radio morphologies (
- Siemiginowska, A., Stanghellini, C., Brunetti, G., Fiore, F., Aldcroft, T. L., Bechtold, J., Elvis, M., Murray, S. S., Antonelli, L. A., & Colafrancesco, S. (2003). Chandra discovery of an X-ray jet and extended X-ray structure in the z = 0.63 Quasar B2 0738+313. Astrophysical Journal Letters, 595(2 I), 643-655.More infoAbstract: We have made a ∼30 ks Chandra observation of the redshift z = 0.63 gigahertz-peaked spectrum (GPS) quasar B2 0738+313. We detected X-ray emission from the core and have discovered a 200 kpc (projected on the sky) X-ray jet. The X-ray jet is narrow and curves, following the extended radio structure to the south of the quasar, and ending with a hot spot at the southernmost part of the radio lobe. The jet has a knot at ∼13″ away from the core. The knot emission is consistent with the X-rays being created by the inverse Compton scattering of the cosmic microwave background (CMB) photons and requires jet bulk Lorentz factors of a few (Γbulk ∼ 5-7). We discuss the emission mechanisms that may be responsible for the jet emission. We present new VLA data of the core and jet, and discuss the relation between the extended radio and X-ray emission. Extended emission observed in several GPS sources has been interpreted as a signature of the source past activity, while the GPS source is young and newly expanded. We argue that B2 0738+313 may be an example of a new class of radio sources similar to the FR II radio galaxies in their high jet bulk velocities, but with a powerful GPS-like nucleus. B2 0738+313 also has two damped Lya systems along the line of sight, at zabs = 0.0912 and 0.2212. We discuss the possible connection between the X-ray absorption (7.2 ± 0.9 × 1020 cm -2) detected in the ACIS spectrum and these two intervening absorbers. We also investigate an extended structure within the central 10″ of the core in the relation to structure seen in the optical.
- Bechtold, J., Dobrzycki, A., Wilden, B., Morita, M., Scott, J., Dobrzycka, D., Tran, K., & Aldcroft, T. L. (2002). A uniform analysis of the Lyα forest at z = 0-5. III. Hubble Space Telescope faint object spectrograph spectral atlas. Astrophysical Journal, Supplement Series, 140(2), 143-238.More infoAbstract: We analyzed the absorption line spectra of all quasars observed with the high-resolution gratings of the Faint Object Spectrograph on board the Hubble Space Telescope. We examined 788 spectra for 334 quasars and present line lists and identifications of absorption lines in the spectra of 271 of them. Analysis of the statistics of the Lyα and metal absorption systems are presented in companion papers. The data and several analysis products are available electronically and on the authors' Web site.
- Dobrzycki, A., Bechtold, J., Scott, J., & Morita, M. (2002). A uniform analysis of the Lyα forest at z = 0-5. IV. The clustering and evolution of clouds at z ≤ 1.7. Astrophysical Journal Letters, 571(2 I), 654-664.More infoAbstract: We present results on the evolution and clustering of Lyα lines at low redshift as part of our series "A Uniform Analysis of the Lyα Forest at z = 0-5." The sample analyzed in this paper contains 1298 Lyα absorption lines from 165 quasar spectra mined from the archives of the Faint Object Spectrograph on the Hubble Space Telescope (HST). Our sample extends to z ≈ 1.7, slightly higher than the sample analyzed by the HST Quasar Absorption Line Key Project. We confirm the result from the Key Project that the number density evolution of Lyα lines at low redshifts can be described by a power law that is significantly flatter than that found at high z. We find that the evolution is somewhat steeper than obtained previously. Specifically, we find γ = 0.54 ± 0.21 for lines with equivalent widths greater than 0.24 Å and γ = 0.60 ± 0.14 using a variable equivalent width threshold. We find that the difference between our and Key Project results is likely attributable to different redshift coverage of the two samples. The results concerning the number density evolution are not significantly affected if one includes Lyα lines which are members of metal systems. Object-to-object fluctuations in the number of lines detected are small, indicating a high degree of uniformity in the intergalactic medium on large scales. We find marginal evidence that weak and strong lines undergo different evolution. We find weak clustering for Lyα lines at velocity separations Δ V ≤ 500 km s-1, weaker than the level predicted from an earlier analysis by Ulmer of a small subsample of the Key Project data. We see no correlations for metal system-Lyα forest or extensive metal system-Lyα forest combinations.
- Scott, J., Bechtold, J., Morita, M., Dobrzycki, A., & Kulkarni, V. P. (2002). A uniform analysis of the Lyα forest AT z = 0-5. V. The extragalactic ionizing background at low redshift. Astrophysical Journal Letters, 571(2 I), 665-692.More infoAbstract: In Paper III of our series, "A Uniform Analysis of the Lyα Forest at z = 0-5," we presented a set of 270 quasar spectra from the archives of the Faint Object Spectrograph (FOS) on the Rubble Space Telescope (HST). A total of 151 of these spectra, yielding 906 lines, are suitable for using the proximity effect signature to measure J(ν0), the mean intensity of the hydrogen-ionizing background radiation field, at low redshift. Using a maximum-likelihood technique and the best estimates possible for each QSO's Lyman limit flux and systemic redshift, we find J(ν0) = 7.6-3.0+9.4 × 10-23 erg s-1 cm-2 Hz-1 sr-1 at 0.03 < z < 1.67. This is in good agreement with the mean intensity expected from models of the background which incorporate only the known quasar population. When the sample is divided into two subsamples, consisting of lines with z < 1 and z > 1, the values J(ν0) found are 6.5-1.6+38. × 10-23 erg s-1 cm-2 Hz-1 sr-1, and 1.0-0.2+3.8 × 10-22 erg s-1 cm-2 Hz-1 sr-1, respectively, indicating that the mean intensity of the background is evolving over the redshift range of this data set. Relaxing the assumption that the spectral shapes of the sample spectra and the background are identical, the best-fit H I photoionization rates are found to be 6.7 × 10-13 s-1 for all redshifts, and 1.9 × 10-13 and 1.3 × 10-12 s-1 for z < 1 and z > 1, respectively. The inclusion of blazars, associated absorbers, or damped Lyα absorbers, or the consideration of a ΛCDM cosmology rather than one in which ΩΛ = 0 has no significant effect on the results. The result obtained using radio-loud objects is not significantly different from that found using radio-quiet objects. Allowing for a variable equivalent width threshold gives a consistently larger value of J(ν0) than the constant threshold treatment, though this is found to be sensitive to the inclusion of a small number of weak lines near the QSO emission redshifts. This work confirms that the evolution of the number density of Lyα lines is driven by a decrease in the ionizing background from z ∼ 2 to z ∼ 0 as well as by the formation of structure in the intergalactic medium.
- Siemiginowska, A., Bechtold, J., Aldcroft, T. L., Elvis, M., Harris, D. E., & Dobrzycki, A. (2002). Chandra discovery of a 300 kiloparsec X-ray jet in the gigahertz-peaked spectrum quasar PKS 1127-145. Astrophysical Journal Letters, 570(2 I), 543-556.More infoAbstract: We have discovered an X-ray jet with Chandra imaging of the z = 1.187 radio-loud quasar PKS 1127-145. In this paper we present the Chandra X-ray data, follow-up Very Large Array observations, and optical imaging using the Hubble Space Telescope Wide Field Planetary Camera 2. The X-ray jet contains 273 ± 5 net counts in 27 ks and extends ∼30″ from the quasar core, corresponding to a minimum projected linear size of ∼330 h50-1 kpc. The evaluation of the X-ray emission processes is complicated by the observed offsets between X-ray and radio brightness peaks. We discuss the problems posed by these observations to jet models. In addition, PKS 1127-145 is a gigahertz-peaked spectrum (GPS) radio source, a member of the class of radio sources suspected to be young or "frustrated" versions of FR I radio galaxies. However, the discovery of an X-ray and radio jet extending well outside the host galaxy of PKS 1127-145 suggests that activity in this and other GPS sources may be long-lived and complex.
- Bechtold, J. (2001). Chandra detection of X-ray absorption associated with a damped Lyα system. Astrophysical Journal Letters, 562(1 PART I), 133-138.More infoAbstract: We have observed three quasars, PKS 1127-145, Q1331+171, and Q0054+144, with the ACIS-S aboard the Chandra X-Ray Observatory in order to measure soft X-ray absorption associated with intervening 21 cm and damped Lyα absorbers. For PKS 1127-145, we detect absorption that, if associated with an intervening zabs = 0.312 absorber, implies a metallicity of 23% solar. If the absorption is not at zabs = 0.312, then the metallicity is still constrained to be less than 23% solar. The advantage of the X-ray measurement is that the derived metallicity is insensitive to ionization, inclusion of an atom in a molecule, or depletion onto grains. The X-ray absorption is mostly due to oxygen and is consistent with the oxygen abundance of 30% solar derived from optical nebular emission lines in a foreground galaxy at the redshift of the absorber. For Q1331+171 and Q0054+144, only upper limits were obtained, although the exposure times were intentionally short, since for these two objects we were interested primarily in measuring flux levels to plan for future observations. The imaging results are presented in a companion paper. © 2001. The American Astronomical Society. All rights reserved. Printed in U.S.A.
- Jian, G. e., Bechtold, J., & Kulkarni, V. P. (2001). H2, C I, Metallicity, and dust depletion in the z = 2.34 damped Lyα absorption system toward QSO 1232+0815. Astrophysical Journal Letters, 547(1 PART 2), L1-L5.More infoAbstract: We report the detection of strong molecular hydrogen (H2) absorption lines in the z = 2.34 damped Lyα absorber (DLA) toward QSO 1232+0815. This is the second detection in our survey for high-redshift molecules. The new ultraviolet spectrum of the QSO 1232+0815 at 0.9 Å resolution, taken with the Multiple Mirror Telescope Blue Channel Spectrograph, shows the v = 0-0 up to 10-0 Lyman bands and also the Werner v = 0-0 band of H2 associated with the z = 2.34 DLA. We have estimated the total H2 column density in this system. It ranges from ≈3 × 1019 cm-2 to ≈3 × 1017 cm-2 depending on the Doppler parameters, b = 6 or 10 km s-1. Based on the best fit with b = 6 km s-1, the estimated kinetic temperature is TK ≈ 80 K. The measurements of the abundance of zinc and iron in the same DLA show that the metallicity measured by the relatively undepleted element zinc is [Zn/H] = -0.86, while the relative abundance ratio [Fe/Zn] is -1.04, indicating dust depletion. Combining our work with previous results on H2 and relative heavy-element depletion, we find that there is a correlation between them, which suggests that the formation of H2 on dust grains is perhaps the dominant formation process in high-redshift DLAs. Detections of strong absorption from the ground and excited states of neutral carbon (C I) in the z = 2.34 DLA are also presented. The excitation temperature between the two fine-structure levels of C I is 15.7 ± 3.5 K, an upper limit for the cosmic microwave background radiation temperature at z = 2.34. This value is consistent with the prediction by the standard big bang cosmology.
- Kuhn, O., Elvis, M., Bechtold, J., & Elston, R. (2001). A search for signatures of quasar evolution: Comparison of the shapes of the rest-frame optical/ultraviolet continua of quasars at z > 3 and z ∼ 0.1. Astrophysical Journal, Supplement Series, 136(2), 225-264.More infoAbstract: For 15 bright (V < 17.5), high-redshift (z > 3) quasars, we have obtained infrared spectra and photometry, and optical spectrophotometry and photometry, which we use to construct their spectral energy distributions (SEDs) from λrest ∼ 1285-5100 Å. High-resolution spectroscopy for seven enable measurements of their continua shortward of Lyα, and L′ detections of four of these extend their SEDs redward to λrest ∼ 7500 Å. We examine the optical/UV continuum shapes and compare these to those of a set of 27 well-studied low-redshift (z ∼ 0.1) quasars which are matched to the high-redshift ones in evolved luminosity. Single power-law fits to the average fluxes within a set of narrow, line-free, windows between 1285 and 5100 Å, but excluding the 2000-4000 Å region of the Fe II + BaC "small bump," are adequate for most of the objects. For both the high- and low-redshift samples, the distributions of spectral indices, αouv (Fv ∼ vαouv) span a wide range, with δαouv ∼ 1. The cause of such diversity is investigated, and our analysis is consistent with the conclusion of Rowan-Robinson: that it arises from differences in both the emitted continua themselves and in the amounts of intrinsic extinction undergone. The mean (median) optical/UV spectral indices for the high- and low-redshift samples are -0.32 (-0.29) and -0.38 (-0.40), respectively. A Student's t-test indicates that these do not differ significantly, and a K-S test shows likewise for the distributions. Assuming the optical/UV continuum derives from accretion, the similarity of the spectral indices at high and low redshift is inconsistent with models which interpret the statistical evolution as resulting from a single generation of slowly dimming quasars and instead favors those involving multiple generations of short-lived quasars formed at successively lower luminosities. A clear difference between the high- and low-redshift samples occurs in the region of "small bump." The power-law fit residuals for the low-redshift sample show a systematic excess from ∼2200 to 3000 Å; but this feature is weak or absent in the high-redshift sample. Further study is needed to determine what is responsible for this contrast, but it could reflect differences in iron abundance or Fe II energy source, or alternatively, an intrinsic turnover in the continuum itself which is present at low but not at high redshift.
- Elvis, M., Fiore, F., Siemiginowska, A., Bechtold, J., Mathur, S., & McDowell, J. (2000). 150 keV emission from PKS 2149-306 with BeppoSAX. Astrophysical Journal Letters, 543(2 PART 1), 545-551.More infoAbstract: A BeppoSAX observation of the z = 2.34 quasar PKS 2149-306 produced a strong signal in the high-energy PDS instrument up to a maximum observed energy of nearly 50 keV, 150 keV in the quasar frame. The BeppoSAX spectrum spans almost three decades (0.3-150 keV, quasar frame) and shows an extremely hard (α = 0.4 ± 0.05) X-ray spectrum above 3 keV (comparable to XJB the X-ray background slope), and either a softer (α = 1.0+0.6-0.3) low-energy component, or an ionized absorber at zero redshift. No evidence is seen of an Fe-K emission line (EW < 167 eV at 6.5 keV quasar frame), a Compton hump (R < 0.3). A bremsstrahlung fit gives kT(rest) = 46+32-16 keV, similar to the X-ray background value, and a high-energy cut off power law requires Ecut > 120 keV (quasar frame). The SED of PKS 2149-306 shows two peaks at ∼ 1012±0.5 Hz and ∼ 1021±1.0 Hz (∼0.3 mm and ∼4 MeV), strongly resembling a low-energy cut off BL Lac object (LBL). The ratio of the two peaks shows an extreme Compton dominance (CD = 1.4 ± 0.4), as in flat-spectrum radio quasars (FSRQs). The presence of an additional "optical/ UV big bump" component may provide photons that cool the jet, suppressing the radio emission.
- Scott, J., Bechtold, J., & Dobrzycki, A. (2000). A uniform analysis of the Lyα forest at z = 0-5. I. The sample and distribution of clouds at z > 1.7. Astrophysical Journal, Supplement Series, 130(1), 37-66.More infoAbstract: We present moderate-resolution data for 39 quasi-stellar objects (QSOs) at z ≈ 2 obtained at the Multiple Mirror Telescope. These data are combined with spectra of comparable resolution of 60 QSOs with redshifts greater than 1.7 found in the literature to investigate the distribution of Lyα forest lines in redshift and equivalent width. We find a value for γ, the parameter describing the number distribution of Lyα forest lines in redshift, of 1.88 ± 0.22 for lines stronger than a rest equivalent width of 0.32 Å, in good agreement with some previous studies. The Kolmogorov-Smirnov test was applied to the data, and it is found that this single power law is a good fit over the relevant redshift ranges. Simulations of the Lyα forest were performed to determine the completeness of the line lists and to test how well the analysis recovers the underlying line statistics, given this level of completeness.
- Scott, J., Bechtold, J., Dobrzycki, A., & Kulkarni, V. P. (2000). A uniform analysis of the Lyα forest at z = 0-5. II. Measuring the mean intensity of the extragalactic ionizing background using the proximity effect. Astrophysical Journal, Supplement Series, 130(1), 67-89.More infoAbstract: Moderate-resolution data for 40 quasi-stellar objects (QSOs) at z ≈ 2 were combined with spectra of comparable resolution of 59 QSOs with redshifts greater than 1.7 found in the literature to form a large, homogeneous sample of moderate-resolution (∼1 Å) QSO spectra. These spectra were presented and the statistics of the Lyα forest were discussed in Paper I. In this analysis, we demonstrate that a proximity effect is present in the data; i.e., there exists a significant (5.5 σ) deficit of lines at zabs ≈ zem. Within 1.5 h-1 Mpc of the QSO emission redshift, the significance does depend on QSO luminosity, in accordance with the theory that this effect is caused by enhanced ionization of hydrogen in the vicinity of the QSO from UV photons from the QSO itself. The photoionization model of Bajtlik, Duncan, & Ostriker permits an estimate of the mean intensity of the extragalactic background radiation at the Lyman limit. We compare the results of this standard analysis with those obtained using a maximum likelihood technique. If the spectrum of the background is assumed to be identical to that of each individual QSO, and if this background is assumed to be constant over the redshift range 1.7 < z < 3.8, then the best-fit value for J(v0) is found to be 1.4+1.1-0.5 × 10-21 ergs s-1 cm-2 Hz-1 sr-1, using QSO redshifts based on the Lyα emission line. Systemic QSO redshifts based on the [O III] λ5007 emission line for 19 objects in our sample show an average redshift of ∼400 km s-1 with respect to Lyα emission. Using redshifts based on [O III] or Mg II for the 35 objects for which they are measured and adding 400 km s-1 to the remaining QSO Lyα redshifts gives a lower value of J(v0), 7.0+3.4-4.4 × 10-22 ergs s-1 cm-2 Hz-1 sr-1. This value is in reasonable agreement with the predictions of various models of the ionizing background based on the integrated quasar luminosity function. Allowing for the fact that individual QSOs have different spectral indices that may also be different from that of the background, we use the standard methods to solve for the H I photoionization rate, Γ, and the parameters describing its evolution with redshift. The best-fit value for the H I ionization rate we derive is 1.9+1.2-1.0, × 10-12 s-1, in good agreement with models of the background that incorporate QSOs only. Finally, we use simulated Lyα forest spectra including the proximity effect to investigate curve-of-growth effects in the photoionization model used in the analysis. We find that the presence of lines on the saturated part of the curve of growth could cause our estimates of the background intensity to be overestimated by a factor of 2-3. This large absorption-line sample and these techniques for measuring the background and understanding the systematics involved allow us to place what we believe are the firmest limits on the background at these redshifts.
- Siemicinowska, A., Bechtold, J., Aldcroft, T. L., Mcleod, K. K., & Keeton, C. R. (1998). Q1208 +1011: Search for the lensing galaxy. Astrophysical Journal Letters, 503(1 PART I), 118-124.More infoAbstract: We present a high-resolution spectrum of the high-redshift, lensed quasar Q1208+1101, obtained with the echellette spectrograph on the Multiple Mirror Telescope. We examine the new and published spectra and provide an updated list of high-confidence metal-line absorption systems at z = 1.1349, 2.8626, 2.9118, 2.9136, and 2.9149. Combining this with a simple model of the gravitational lens system allows us to constrain the possible lens redshifts. The high-redshift (z > 2.5) and low-redshift (zlt; 0.4) candidates can be ruled out with high confidence. The current spectra effectively probe about 40% of the redshift range in which the lens is expected. In that range, there is only one known metal-line absorption system, an Mg II absorber at z = 1.1349. We consider the possibility that this system is the lensing galaxy and discuss the implied parameters of the galaxy. © 1998. The American Astronomical Society. All rights reserved.
- Bechtold, J., Yee, H. K., Elston, R., & Ellinoson, E. (1997). Hα imaging of the candidate protogalaxy MS 1512-cB58. Astrophysical Journal Letters, 477(1 PART II), L29-L32.More infoAbstract: We have obtained an image of the candidate protogalaxy MS 1512-cB58 through a narrow passband filter centered on Hα redshifted to z = 2.72. MS 1512-cB58 shows excess emission that is spatially extended, has a rest equivalent width of 56.7 Å, and luminosity of 3 × 1043 h-275 ergs s-1 (q0 = 0.1). Assuming that the excess emission arises from nebular Hα associated with H II regions, the observed luminosity implies a star formation rate of 285 M⊙ yr-1 (neglecting any possible magnification by gravitational lensing). By comparison, the luminosity of the stellar continuum at 1500 Å, along with models for the spectral energy distribution, indicate a star formation rate about a factor of 12 greater. We discuss plausible explanations for this discrepancy and possible future observations that may clarify the situation. 1997 The American Astronomical Society. All rights reserved.
- Frayer, D. T., Papadopoulos, P. P., Bechtold, J., Seaquist, E. R., Yee, H. K., & Scoville, N. Z. (1997). Constraining the molecular gas reservoir associated with the protogalaxy candidate MS1512-cB58. Astronomical Journal, 113(2), 562-568.More infoAbstract: We report on sensitive searches for molecular CO(3-2) emission from the recently discovered protogalaxy candidate MS1512-cB58 (cB58) at a redshift of z = 2.72. The rest-frame UV light from cB58 indicates that a large burst of star formation (Mstars∼4 x 1010h-275M⊙) has occurred within less than 108 yr. The limit on the CO line intensity is S(CO)
- Jian, G. E., Bechtold, J., Walker, C., & Black, J. H. (1997). Spectroscopy of PKS 0528-250: New limits on CO absorption and emission. Astrophysical Journal Letters, 486(2 PART I), 727-737.More infoAbstract: We have obtained a moderate-resolution spectrum of the quasar PKS 0528 -250 with the Red Channel Spectrograph on the Multiple Mirror Telescope in order to study a damped Lyα absorption-line system at z = 2.8115. We obtain a new upper limit for the CO column density for the z = 2.8108 velocity component in the z = 2.8115 damped Lyα system. The ionization of different species in this component rules out a quasar spectral energy distribution as the ionization field and implies an ultraviolet radiation field intensity a few times that of the Milky Way value. The estimated total number density is n(H) ∼ 20 cm-3. The physical size for the z = 2.8108 component implied by these models is about 40 pc. The ionization of different species also suggests a structure with a hot intercloud medium associated with a H i cloud in this component, that is, most low ionized ions are from the cold medium where photoionization and photodissociation dominates. The highly ionized species may be from the intercloud medium where collisional ionization dominates. We also present newly identified Ni H absorption lines in the z = 2.1408 and z = 2.8115 damped Lyα systems. The derived depletion of nickel by dust confirms previous results that the dust-to-gas ratio in these two damped Lya systems is about 10% of the Milky Way ratio. Millimeter-wavelength observations obtained at the NRAO 12 m telescope provide new upper limits on CO (3-2) emission in the z = 2.8115 damped Lyα system. © 1997. The American Astronomical Society. All rights reserved.
- Jian, G. e., & Bechtold, J. (1997). Molecular hydrogen absorption in the z = 1.97 damped Lyα absorption system toward quasi-stellar object Q0013-004. Astrophysical Journal Letters, 477(2 PART II), L73-L77.More infoAbstract: We present a new ultraviolet spectrum of the quasi-stellar object Q0013-004 with 0.9 Å resolution obtained with the Multiple Mirror Telescope Blue Spectrograph. The v = 0-0, 1-0, 2-0, and 3-0 Lyman bands of H2 associated with the z = 1.9731 damped Lyα absorption-line system have been detected. The H2 column density is N(H2) = 6.9(±1.6) × 1019 cm-2, and the Doppler parameter b = 15 ± 2 km s-1. The populations of different rotational levels are measured and used to derive the excitation temperatures. The estimated kinetic temperature TK ∼ 70 K, and the total particle number density n(H) ∼ 300 cm-3. The UV photoabsorption rate β0 ∼ 6.7 × 10-9 s-1, about a factor of a few times greater than that in a typical diffuse Milky Way interstellar cloud. The total hydrogen column density is N(H) = 6.4(±0.5) × 1020 cm-2. The fractional H2 abundance f = 2N(H2)/[2N(H2) + N(H I)] ∼ 0.22 ± 0.05 is the highest among all observed damped Lyα absorbers. The high fractional H2 abundance is consistent with the inferred presence of dust and strong C I absorption in this absorber. © 1997. The American Astronomical Society. All rights reserved.
- Jian, G. e., Bechtold, J., & Black, J. H. (1997). A new measurement of the cosmic microwave background radiation temperature at z = 1.97. Astrophysical Journal Letters, 474(1 PART I), 67-73.More infoAbstract: We present detections of absorption from the ground state and excited states of C I in the z = 1.9731 damped Lyα system of the QSO 0013-004. The excitation temperature between the J = 0 and J = 1 fine-structure levels of C I is 11.6 ± 1.0 K. We estimate other contributions to the excitation of the C I fine-structure levels, and use the population ratio of the excited state to the ground state to derive an estimate for the cosmic microwave background radiation (CMBR) temperature of T = 7.9 ± 1.0 K at 0.61 mm and z = 1.9731, which is consistent with the predicted value of T = 8.105 ± 0.030 K from the standard cosmology. © 1997. The American Astronomical Society. All rights reserved.
- Khare, P., Srianand, R., York, D. G., Green, R., Welty, D., Huang, K., & Bechtold, J. (1997). The Lyman alpha forest towards B2 1225 + 317. Monthly Notices of the Royal Astronomical Society, 285(1), 167-180.More infoAbstract: We present observations of the Lyman alpha (Ly α) forest towards B2 1225 + 317 taken at a resolution of 18 km s -1. A clean sample of Ly α forest lines is extracted after a careful profile-fitting analysis and the removal of the absorption lines of heavy elements. The sample is analysed for statistical properties. Eighty per cent of the column densities are < 10 14 cm -2. A single power law is inconsistent with the column density distribution and a steepening/break in the distribution is indicated. The average velocity dispersion parameter is 29.4 km s -1. We find 3σ evidence for a correlation between column density and the velocity dispersion parameter. The correlation, however, is mainly the result of narrow lines and weakens to 1.2σ if lines with a velocity dispersion parameter smaller than 20 km s -1 are excluded. An excess of line pairs with velocity separation ≤ 100 km s -1 over the expected number is found. © 1997 RAS.
- Carone, T. E., Peterson, B. M., Bechtold, J., Bertram, R., Bischoff, K., Dietrich, M., Filippenko, A. V., Ho, L. C., Huchra, J. P., Kollatschny, W., Korista, K. T., Matheson, T., Pogge, R. W., Shields, J. C., Smith, P. S., Wagner, R. M., & Wilkes, B. J. (1996). Optical continuum and emission-line variability of the seyfert 1 galaxy markarian 509. Astrophysical Journal Letters, 471(2 PART I), 737-747.More infoAbstract: We report on the results of a 5 year coordinated program of spectroscopic monitoring of the luminous Seyfert 1 galaxy Markarian 509. The Hβ and He II β4686 emission lines are found to respond to continuum variations with time lags of ∼80 and ∼60 days, respectively, considerably longer than the emission-line lags measured for other Seyfert galaxies. © 1996. The American Astronomical Society. All rights reserved.
- Djorgovski, S. G., Pahre, M. A., Bechtold, J., & Elston, R. (1996). Identification of a galaxy responsible for a high-redshift Lyman-α absorption system. Nature, 382(6588), 234-236.More infoAbstract: Damped Lyman-α systems are high-column-density intergalactic clouds of hydrogen, the existence of which is inferred from absorption lines appearing in the emission spectra of distant quasars. The galaxies believed to be responsible for these absorption systems have been suggested as possible progenitors of the normal disk galaxies observed in the local Universe. Indeed, Lyman-α systems appear to contain a substantial fraction of the baryons known to exist in galaxies today. Here we report the optical detection of a galaxy (designated DLA2233 + 131) associated with a known damped Lyman-α absorption system at a redshift of z = 3.150. The properties of this galaxy correspond closely to those expected of a young disk galaxy in the early stages of formation, and show no evidence for an active nucleus. This finding gives strong support to the idea that damped Lyman-α systems represent a population of young galaxies at high redshifts.
- Dobrzycki, A., & Bechtold, J. (1996). Simulation analysis of Lyα forest spectra. I. Empirical description at z ≈ 3. Astrophysical Journal Letters, 457(1 PART I), 102-110.More infoAbstract: We present moderate-resolution (∼50 km s-1 FWHM) spectra of the Lyα forest for seven quasars with redshifts ranging from 2.53 to 3.13, obtained with the Blue Spectrograph and photon-counting Reticon at the Multiple Mirror Telescope. Combined with spectra of 10 other quasars presented elsewhere, we have characterized the distribution of cloud properties in a way which was designed to minimize any subjective part of the analysis. We used artificial absorption spectra, with the same resolution, sampling and signal-to-noise ratio as a function of wavelength as the actual data. Distributions of the physical parameters of the Lyα clouds, namely, the neutral hydrogen column density (N) and Doppler parameter (b), were approximated with dN/dN ∝ N-β and dN/db ∝ exp [-(b - 〈6〉)2/2 σb2], respectively. We constructed a grid of simulated spectra with different input parameters. Comparison of properties of the simulated spectra with the observed spectra yielded acceptable ranges of parameters. Our technique differs from previous similar work in that we use the information contained in the distribution of the strength of the absorption in each resolution element and the distribution of separations between absorption complexes. We derive β = 1.4 ± 0.1 for N ranging from 1013 to 1016 cm-2 and 〈b〉 = 30 ± 15 km s-1. Most previous studies based on line lists indicated β = 1.7-1.9. We attribute this difference to flattening of the column density distribution for low N, recently confirmed by higher resolution observations. Our result for 〈b〉, though consistent with values quoted in the literature, is of lower significance, since it is less than the resolution of our spectra. We conclude by commenting on the importance of line blending in data sets of this kind. © 1996. The American Astronomical Society. All rights reserved.
- Ellingson, E., Yee, H. K., Bechtold, J., & Elston, R. (1996). Optical-IR spectral energy distribution of the protogalaxy candidate MS 1512-cB58. Astrophysical Journal Letters, 466(2 PART II), L71-L74.More infoAbstract: The spectral energy distribution of the protogalaxy candidate MS 1512-cB58 at z = 2.72 is presented. Photometry in seven bands ranging from g to K' (1300-6000 A rest wavelength) are fitted with population synthesis models. The data confirm a very young age for this galaxy in agreement with ages estimated from preliminary C IV λ1550 P Cygni profile modeling. Single-burst models with ages greater than about 20 Myr can be discarded at the 99% confidence level, and continuous star formation models with ages greater than about 35 Myr can be discarded at the 95% confidence level. The spectral energy distribution is most consistent with a continuous star formation model of about 10-20 Myr, with reddening of E(B-V) ∼ 0.3. No evidence for an older population of stars is seen, but the possibility of an older population with as much as 90% of the galaxy mass cannot be ruled out. We discuss the possible ramifications of a nonstandard IMF and gravitational lensing on the galaxy's age and mass. © 1996. The American Astronomical Society. All rights reserved.
- Fang, Y., Duncan, R. C., P., A., & Bechtold, J. (1996). The size and nature of lyman-α forest clouds probed by QSO pairs and groups. Astrophysical Journal Letters, 462(1 PART I), 77-88.More infoAbstract: Closely separated QSO pairs and groups make it possible to probe the size, geometry, and spatial clustering of Lyα forest clouds. Recent spectroscopic observations of Q1343+2640A/B give evidence that the transverse sizes of Lyα clouds are very large at redshifts ≈2 (as reported by Bechtold et al. in 1994). In this paper, we describe a robust Bayesian statistical method for determining cloud sizes in spherical and in thin disk geometries, apply this method to the available data, and discuss implications of our results for models of Lyα clouds. Under the assumption of a population of uniform-sized and unclustered Lyα clouds, the data from Q1343+2640A/B give a 99% confidence lower and upper bounds 61 < R ω 533 h-1 kpc on the radius of spherical clouds at z ≈ 1.8, with a median value of 149 h-1 kpc [(Ω0, Λ0) = (1, 0), and h ≡ H0/100 km s-1 Mpc-1]. The baryonic mass of such large clouds, if they are roughly homogeneous and quasi-spherical, is comparable to the baryonic mass of dwarf irregular galaxies. Their cosmic overdensity is close to the turnaround density but generally below the virialization density, which suggests a population of gravitationally bound but unvirialized protogalactic objects at z ≈ 2. The comoving volume density of these clouds is similar to that of the faint blue galaxies (FBGs) at the limiting magnitude B ≈ 26-27, if these FBGs are distributed approximately over the range of redshift from 0.8 to 2. The timescale for dynamical collapse of overdensities like these clouds is also comparable to the cosmic time difference between z ≈ 2 and z ≈ 1. Both populations of objects show similar weak clustering in space. All this evidence suggests a possible identification of Lyα clouds as the collapsing progenitors of the FBGs at z ∼ 1. We also investigate the other closely separated QSO pairs with published high-quality spectra: Q0307-1931/0307-1932, Q0107-0232/0107-0235, and the triplet of Q1623+268. Imposing a uniform W0 ≥ 0.4 Å counting threshold on all the line lists, we find a trend of larger inferred cloud radius with larger proper separation of QSO pairs, significant at the 3.4 σ level. This indicates that the idealization of unclustered, uniform-sized spherical clouds does not accurately describe the Lyα cloud population. Present data are insufficient to resolve with confidence whether this effect is due to clustering, filamentary shape, or nonuniform cloud size. There is a suggestion, however, that at low redshifts a residual population of larger clouds remains. © 1996. The American Astronomical Society. All rights reserved.
- Kulkarni, V. P., Huang, K., Green, R. F., Bechtold, J., Welty, D. E., & York, D. G. (1996). Pruning the Lyman α forest of Q1331 +170. Monthly Notices of the Royal Astronomical Society, 279(1), 197-218.More infoAbstract: We present a study of the Lyman α forest of the QSO 1331 + 170 in the range 1.67 < Zabs < 2.10 at 18 km s-1 resolution. Our analysis includes a careful search for previously unidentified heavy-element systems, and incorporates detailed deblending of Lyα forest lines from heavy-element lines. Various statistical properties of Lyα forest lines, such as distributions of equivalent widths, H I column densities, Doppler parameters and pair-velocity separations, are computed. The effect on these properties of employing different limiting approaches to heavy-element deblending, and profile-fitting of the lines, is illustrated. Our data suggest that the NH1 distribution may not be fitted adequately by a single power law, i.e., that there may be a relative deficit of strong lines as compared with the predictions of a single power law. However, larger samples are required to verify this deficit. The median b value is ≈ 32 km s-1. No significant correlation is observed between NH1 and b. An excess on the scale of ∼ 100 km s-1 is seen in the pair-velocity correlations, at the level of ∼ 2.6σ for the conservative sample and at the level of ∼ 4.9σ for the less conservative sample. Marginal excess correlation is seen in both the samples at the ≳ 2σ level on scales of ∼ 800-1000 km s-1, and also on scales of ∼ 6000 km s-1.
- Tanner, A. M., Bechtold, J., Walker, C. E., Black, J. H., & Cutri, R. M. (1996). A study of quasar absorption-line systems with IRAS. Astronomical Journal, 112(1), 62-72.More infoAbstract: A survey of quasar absorbers was conducted using the Infrared Astronomical Satellite (IRAS) database. Quasars with known intervening absorption-line systems and broad absorption line (BAL) QSOs were selected primarily from Junkkarinen et al. [ApJ, 77, 203 (1991)]. Of the 570 quasars with IRAS data, 52 showed 3σ or better detections in at least one band in SCANPI analysis. The origin of the IRAS flux could be from the absorption-line systems, other galaxies, or the quasar itself. The spectral energy distributions for quasars detected in the absorption-line sample and BAL QSOs were found to be redder than those of two control samples which suggests that some of the IRAS flux may arise in dust associated with the intervening galaxies. IRAS SUPERSCANPI processing was carried out for 77 quasars with known Mg II absorption at zabs < 1 to investigate the ensemble far-infrared properties of these objects. SUPERSCANPI processing evaluates the median flux for many different positions on the sky, resulting in an improvement in the effective sensitivity. A control sample consisting of objects with no Mg II absorption known at zabs < 1 but with the same distribution of absolute V-magnitude, zem and radio-loud fraction for the background quasars was also processed. The Mg II sample was detected at 3σ or better in all four IRAS bands with a significantly larger flux than the control sample at 60 μm and 100 μm. If this far-infrared emission is from the absorber galaxies, then the far-infrared luminosity of the composite Mg II absorber was found to be comparable to that of a starbursting galaxy, although such a high star-formation rate is inconsistent with the optical and near-infrared colors of low-redshift Mg II systems. Four of the quasars with individual IRAS detections have intervening galaxies identified with the Mg II absorption-lines. The spectral energy distributions of these galaxies imply far-infrared luminosities in excess of what Arp 220 would give at their redshifts. While all the external evidence suggests that the detection of far-infrared emission from the absorber sample may not be connected to the presence of the Mg II absorber, we discuss future observations which may help explain our results. © 1996 American Astronomical Society.
- Yee, H. K., & Bechtold, J. (1996). Variability in the gravitational lens system B1422+231. Astronomical Journal, 111(3), 1007-1012.More infoAbstract: Images of the gravitational lens system B1422+231 in Gunn r and g have been obtained using the subarcsec imaging spectrograph (SIS) at the Canada-France-Hawaii Telescope (CFHT). The photometry is compared with that obtained using the same photometric system one year earlier. Relative positions and fluxes are determined with improved accuracy. It is found that a variation of 0.12±0.02 mag has occurred in the three brightest components. The flux ratios of the components are identical to those measured in the earlier epoch data. This indicates that the different flux ratio of component A to B in the radio observation of an earlier epoch was most likely not the true ratio. The prospect of using the variability of B1422+231 to obtain time delay measurements for the purpose of determining the Hubble constant is discussed. © 1996 American Astronomical Society.
- Yee, H. K., Ellingson, E., Bechtold, J., Carlberg, R. G., & Cuillandre, J. -. (1996). A proto-galaxy candidate at z = 2.7 discovered by its young stellar population. Astronomical Journal, 111(5), 1783-1794.More infoAbstract: A proto-galaxy candidate at z = 2.72 has been discovered serendipitously by the CNOC cluster redshift survey. The candidate is an extremely luminous (V = 20.5 mag, absolute mag -26) and well resolved (2″ × 3″) disk-like galaxy. The redshift is identified from a dozen strong UV absorption lines, including lines with P-Cygni profiles, which are indicative of the presence of young O and B stars. No emission lines are found between 1000 and 2000 Å (rest), including Lyα. The surface brightness profile of the galaxy fits an exponential law with a scale length of ∼3.5 kpc. The multi-color photometric data fit the spectral energy distributions of a stellar population from 400 million years to an arbitrary young age, dependent on the amount of dust extinction. However, the presence of a strong P-Cygni profile in QIVλ 1550 indicates that a very substantial component of the stellar population must be younger than ∼10 Myr. These models predict that this galaxy will evolve into a bright galaxy of several L* in brightness. We can interpret this object as an early type galaxy observed within about 100 million years of the initial burst of star formation which created most of its stellar mass, producing the extremely high luminosity. Because of the resolved, regular, and smooth nature of the object, it is unlikely that the high luminosity is due to gravitational lensing. We estimate the sky density of this type of objects observable at any one time to be 100±1 per square degree. © 7996 American Astronomical Society.
- Bechtold, J., & Yee, H. K. (1995). High spatial resolution spectroscopy of the Lyα absorption towards the gravitational lens system B1422+2309. Astronomical Journal, 110(5), 1984-1992.More infoAbstract: We have obtained spectroscopy of individual components of the gravitational lensed quasar B1422+2309 using the Subarcsecond Imaging Spectrograph at the Canada-France-Hawan Telescope. The quasar has a redshift of 3.62, with four lensed images within a diameter of 1.3″. Components B and C have nearly identical spectra, confirming that they are the gravitationally lensed images of a single quasar. Numerous absorption lines, most of which are attributable to Lyα, are seen in both spectra. All lines detected are seen in the spectra of both components, implying that the Lyα forest clouds are larger than 0-0.15h100-1 kpc at z≈3.5. The equivalent widths of common lines are highly correlated, but the differences in the equivalent widths are larger than what is expected from the statistical errors in the individual lines. The scatter in the differences in equivalent widths can be accounted for if the column densities between the two lines of sight differ on average by approximately a factor of 1.5. This suggests that there are small-scale inhomogeneities in the gas density of the structures causing Lyα forest absorption. © 1995 American Astronomical Society.
- Lowenthal, J. D., Hogan, C. J., Green, R. F., Woodgate, B., Caulet, A., Brown, L., & Bechtold, J. (1995). Imaging and spectroscopy of damped Lyα quasi-stellar object absorption-line clouds. Astrophysical Journal Letters, 451(2), 484-497.More infoAbstract: We present the results of a multifaceted search for line emission from the vicinities of high-redshift quasi-stellar object (QSO) absorption-line clouds, most of them damped Lyα systems at z ≳ 2. Seven fields containing QSOs with known intervening damped Lyα absorbers were imaged with the GSFC Fabry-Perot Imager to search for diffuse redshifted Lyα. Apart from the one Lyα companion galaxy reported previously, no confirmed extended Lyα emission was detected down to 3 σ flux levels of around 3 x 10-17 ergs s-1 cm-2, corresponding to star formation rates ≲1 M⊙ yr-1, assuming case B recombination, a reasonable initial mass function, and negligible extinction by dust. One of the damped Lyα systems studied here, toward Q0836+113, has been reported to show faint, extended Lyα emission. While our Lyα images of that field are not sensitive enough to confirm the reported flux levels, we did detect and spectroscopically confirm redshifted [O II] λ3727 and continuum emission from a closer intervening system, a Mg II system at z = 0.788, at the same spatial position as the reported Lyα emission from the more distant object, and we suggest the possibility that all the observations of this field can be explained by the closer system alone. Six damped Lyα systems, including two that were imaged with the Fabry-Perot, were also imaged with two-dimensional long-slit CCD spectroscopy at ∼2 Å resolution in the core of the Lyα absorption line. No convincing Lyα emission was found from any of the systems, including Q0836+113, for which our sensitivity was again insufficient to confirm the previously reported extended Lyα emission. However, there is yet another independent claim of Lyα emission from that cloud, but spatially unresolved, in conflict with the report of extended emission; our observations do not reproduce the report of compact Lyα emission, which should have appeared at about the 7 σ level. Although observationally allowable quantities of dust in the damped Lyα clouds can in some cases quench Lyα flux by up to several orders of magnitude, several of the damped clouds studied here are arguably metal and dust poor, leading us to believe that our limits on Lyα emission generally constrain the star formation rates to be ≲10 M⊙ yr-1, comparable to normal Sc galaxies today. Whatever their exact nature, the damped Lyα clouds therefore appear not to be spectacular primeval galaxies seen in the act of forming a galaxy's worth of stars.
- Aldcroft, T. L., Bechtold, J., & Elvis, M. (1994). Mg II absorption in a sample of 56 steep-spectrum quasars. Astrophysical Journal, Supplement Series, 93(1), 1-46.More infoAbstract: We present an analysis of the statistical properties of Mg II absorbers found in the spectra of 56 intrinsically faint, steep-spectrum radio quasars. We observe for the first time a significant excess of associated Mg II absorbers over the number expected from cosmologically distributed absorbers. This result is in contrast to previous Mg II surveys in which the QSOs were optically selected. This distinction is similar to the result for associated C IV absorbers, in which intrinsically faint, steep-spectrum quasars show excess associated absorption and intrinsically bright QSOs (both radio-loud and radio-quiet) do not show an excess. From our spectra a statistically complete list of absorption lines is derived, and we find 29 Mg II absorbers, 18 of which have not been previously reported. We also determine several characteristics of the quasar emission lines in our spectra. The Mg II absorber distribution as a function of redshift and equivalent width is calculated both for our sample alone and from our sample combined with spectra from other surveys. For the redshift distribution n(z) = n(1 + z)γ, we obtain, using the combined sample, the values γ = 1.11 ± 0.46 for Wmin = 0.6 Å and γ= 2.47 ± 0.68 for Wmin = 1.0 Å. We find that the distribution of strong absorbers is inconsistent with no evolution at a confidence level between 2.2 and 2.9 σ, depending on the deceleration parameter q0. The deviation from no evolution is similar to what had been previously reported. © 1994 The American Astronomical Society. All rights reserved.
- Bechtold, J. (1994). THE Lyman-alpha forest near 34 Quasi-Stellar Objects with z > 2.6. Astrophysical Journal, Supplement Series, 91(1), 1-78.More infoAbstract: Moderate-resolution spectra of 34 high-redshift QSOs were obtained at the Multiple Mirror Telescope and Palomar 5 m Telescope in order to study the properties of the Lyα forest absorption lines with zabs ≈ zem. For zabs ≪ zem, the evolution of the number of lines per unit redshift, dN/dz, is well described by the form (1 + z)γ, with γ = 1.89 ± 0.28 for lines with rest equivalent width greater than 0.32 Å. For lines stronger than 0.16 Å, γ = 1.32 ± 0.24. These results imply slower evolution in the mean free path for absorption for the clouds than previously thought. When this sample is combined with HST results for low redshift (Bahcall et al. 1993), a single γ is an acceptable fit to the data, with γ = 1.26 ± 0.13 for zabs = 0-4.1, although an inflection at z ≈ 1.5 may be present. In the high-redshift sample, there is a significant trend of decreasing γ with decreasing equivalent width limit, or, alternatively, a change in equivalent width distribution with redshift. There is no significant curvature in the log (dN/dz) versus log (1 + z) relation for the strong lines, but some steepening of γ at z ≈ 2.5 for the weak ones. While these findings for the weak lines are highly significant in a statistical sense, they may result from some subtle line-blending problem, rather than a real physical process. The lines with zabs ≈ zem are significantly depleted. The strength of the deficit of lines depends weakly on QSO Lyman limit luminosity, but not redshift. The strength of the deficit also depends on the rest equivalent width of the lines, with weak lines showing a relatively weaker effect. These findings support previous suggestions that the "proximity effect" results from enhanced photoionization by the QSO's EUV radiation, rather than some property of the QSO or intergalactic medium which evolves with redshift. The simple photoionization model of Bajtlik, Duncan, & Ostrīker describes the data well. If the ionizing background at the Lyman limit, Jv, is assumed to be constant with redshift for 1.6 < z < 4.1, and writing Jv = J-21 × 10-21 ergs cm-2 s-1 Hz-1 sr-1, then J-21 ≈ 3. This value is formally consistent with previous results, although about a factor of 3 larger. Hence, the factor by which QSOs fail to provide the EUV background at high redshifts (at least in this simple picture), is also increased. If the redshift dependence of Jv is parameterized as Jv ∝ (1 + z)j, then j is not well constrained owing to the small redshift interval sampled, and acceptable fits are obtained for -7 < j < 4. Additions to the simple model and the resulting uncertainties in these estimates of Jv are discussed. One serious uncertainty is the neutral fraction of the clouds. If the clouds are nearly neutral, then Jv must be implausibly low, J-21 ≈ 0.01, in order to account for the proximity effect observed in this sample. In addition, if the systemic redshifts of the QSOs are systematically underestimated, then J-21 may be up to a factor of ∼3 smaller. Given these uncertainties, the J-21 at z ≈ 3 derived from the proximity effect is in reasonable agreement with the expected contribution of luminous QSOs. © 1994. The American Astronomical Society. All rights reserved.
- Bechtold, J., P., A., Duncan, R. C., & Fang, Y. (1994). Spectroscopy of the double quasars Q1343+266A, B: A new determination of the size of Lyman-alpha forest absorbers. Astrophysical Journal Letters, 437(2 PART 2), L83-L86.More infoAbstract: We have obtained spectroscopy of Q1343+266A, B, a pair of quasars at redshift z = 2.03 with a projected separation of 9″.5. This system is well suited for probing the Lyα forest, since the two-component spectra show several Lyα lines in common and several others not. Using Bayesian statistics, under the idealization of uniform-radius spherical absorbers, we find that the Lyα cloud radius at z ≈ 1.8 lies in the range 40 h-1 kpc < R < 280 h-1 kpc with 98% confidence in a (Ω0, Λ0) = (1, 0) model universe, where h ≡ (H0/100 km s-1 Mpc-1). The median value of R is 90 h-1 kpc. These numbers scale up by a factor 1.44 for (Ω0, Λ0) = (0.1, 0) and by a factor 1.85 for (0.1, 0.9). Pressure-confined and freely expanding Lyα cloud models in which the absorbers formed in a significantly more compressed state at z ≫ 2 are contradicted by these new data, as are models involving stably confined gas concentrations in photoionization equilibrium within minihalos of cold dark matter. The comoving density of Lyα forest objects at z ∼ 2 is ∼0.3 h (R/100 kpc)-2 Mpc-3 in a (1, 0) model universe. This suggests a possible identification of Lyα clouds with the unvirialized, collapsing progenitors of the faint, blue galaxies at z ∼ 1.
- Ellingson, E., Yee, H. K., Bechtold, J., & Dobrzycki, A. (1994). Metal-line absorption at zabs∼zem from associated galaxies. Astronomical Journal, 107(4), 1219-1226.More infoAbstract: For a preliminary study of whether C IV absorption at zabs∼zem is related to associated galaxy companions, we have collected data from a sample of 10 quasars with 0.15
- Elvis, M., Fiore, F., Wilkes, B., Mcdowell, J., & Bechtold, J. (1994). Absorption in X-ray spectra of high-redshift quasars. Astrophysical Journal Letters, 422(1), 60-72.More infoAbstract: We present evidence that X-ray absorption is common in high-redshift quasars. We have studied six high-redshift (z ∼ 3) quasars with the ROSAT PSPC of which four are in directions of low Galactic NH. Three out of these four show excess absorption, while only three in ∼ 50 z ≲ 0.4 quasars do, indicating that such absorption must be common, but not ubiquitous, at high redshifts, and that the absorbers must lie at z > 0.4. The six quasars were: S5 0014+81, Q0420-388, PKS 0438-436, S4 0636+680. PKS 2000-330, PKS 2126-158, which have redshifts between 2.85 and 3.78. PKS 0438-436 and PKS 2126-158 show evidence for absorption above the local Galactic value at better than 99.999% confidence level. If the absorber is at the redshift of the quasar, then values of NH = [0.86(+0.49, -0.28)] × 1022 atoms cm-2 for PKS 0438-436, and NH = [1.45(+1.20, -0.64)] × 1022 atoms cm-2 for PKS 2126-158, are implied, assuming solar abundances. The spectrum of S4 0636+680 also suggests the presence of a similarly large absorption column density at the 98% confidence level. This absorption reverses the trend for the most luminous active galactic nuclei (AGN) to have the least X-ray absorption, so a new mechanism is likely to be responsible. Intervening absorption due to damped Lyα systems is a plausible cause. We also suggest, as an intrinsic model, that intracluster material, e.g., a cooling flow, around the quasar could account for both the X-ray spectrum and other properties of these quasars. All the quasars are radio-loud and three are gigahertz peaked (two of the three showing absorption). No excess absorption above the Galactic value is seen toward Q0420-388. This quasar has two damped Lyα systems at z = 3.08. The limit on the X-ray column density implies a low ionization fraction, N(H I)/N(H) ≳ 4 × 10-3 (3 σ), for solar abundances, for these systems, and can set a weak limit on the size of the absorber. In the emitted frame these PSPC spectra cover the band ∼0.5-10 keV, which has been well observed for low-redshift quasars and AGN. Comparison of high and low-redshift spectra in this emitted band shows no change of mean spectral index greater than ΔαE > 0.3 (99% confidence) with either redshift or luminosity, for radio-loud quasars.
- Elvis, M., Wilkes, B. J., Mcdowell, J. C., Green, R. F., Bechtold, J., Wlllner, S. P., Oey, M. S., Polomski, E., & Cutri, R. (1994). Atlas of quasar energy distributions. Astrophysical Journal, Supplement Series, 95(1), 1-68.More infoAbstract: We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, and 18 are radio loud. The SEDs are presented both in figures and in tabular form, with additional tabular material published on CD-ROM. Previously unpublished observational data for a second set of quasars excluded from the primary sample are also tabulated. The effects of host galaxy starlight contamination and foreground extinction on the UVSX sample are considered and the sample is used to investigate the range of SED properties. Of course, the properties we derive are influenced strongly by the selection effects induced by quasar discovery techniques. We derive the mean energy distribution (MED) for radio-loud and radio-quiet objects and present the bolometric corrections derived from it. We note, however, that the dispersion about this mean is large (∼one decade for both the infrared and ultraviolet components when the MED is normalized at the near-infrared inflection). At least part of the dispersion in the ultraviolet may be due to time variability, but this is unlikely to be important in the infrared. The existence of such a large dispersion indicates that the MED reflects only some of the properties of quasars and so should be used only with caution.
- P., A., Bechtold, J., Fang, Y., & Duncan, R. C. (1994). Spectroscopy of the double quasars Q1343+266A, B: The relationship between galaxies and quasi-stellar object C IV absorption lines. Astrophysical Journal Letters, 437(2 PART 2), L79-L82.More infoAbstract: We present spectra of QSOs Q1343+266A, B, covering Lyβ to C IV emission at 2 Å resolution, and find further evidence that this system is not gravitationally lensed. We see, however, a large number of Lyα and some C IV absorption features common to both spectra. The frequency of C IV lines in common indicates that these absorbers have a radius close to the sight line separation, 39 h-1 kpc (q0 = 0.5), implying a spatial number density of these absorbers the same as current-day L > 0.3 L* galaxies. Furthermore, the velocity mismatch for C IV systems indicates absorber masses in the range 1011 M⊙ < M < 1012 M⊙. These results confirm that typical galaxies cause QSO C IV-line absorption.
- Tripp, T. M., Bechtold, J., & Green, R. F. (1994). Spectral energy distributions of the brightest palomar-green quasars at intermediate redshifts. Astrophysical Journal Letters, 433(2), 533-552.More infoAbstract: We have combined low-dispersion International Ultraviolet Explorer (IUE) spectra with the optical/near-IR spectrophotometry of Neugebauer et al. (1987) in order to study the spectral energy distributions of seven of the brightest Palomar-Green quasars at intermediate redshifts (0.9 ≤ zem ≤ 1.5). Some of these PG quasars are barely detectable in long IUE exposures, so we have used the Gaussian Extraction (GEX) technique to maximize the signal-to-noise of the IUE data, and we have co-added all spectra available from the IUE archive for each QSO unless the ultraviolet spectra varied significantly from one exposure to the next. We have corrected the spectral energy distributions for Milky Way reddening using the observed neutral hydrogen column densities on each sight line and the gas-to-dust relation recently derived by Diplas & Savage. Six of the seven quasars are detected down to λ ≪ 700 Å in the rest frame, and consequently continuum reddening due to dust in the immediate vicinity of the quasar can have a dramatic effect on the spectral energy distributions, even if the intrinsic E(B-V) is very small by Galactic standards. In order to explore the possible importance of intrinsic continuum reddening, we have assembled a heuristic extinction curve which extends to λ ≪ 912 Å. Since the 2200 Å bump has never been detected in quasar spectra, longward of the Lyman limit our heuristic extinction curve is based on the Small Magellanic Cloud extinction curve (which contains very little 2200 Å bump). Shortward of the Lyman limit, our extinction curve smoothly increases down to λ ≈700 Å (hv ≈ 18 eV) and then turns over in crude accordance with theoretical work based on the Kramers-Kronig relations and laboratory studies. Using this heuristic extinction curve, we derive reasonable upper limits on the intrinsic E(B -V) for each quasar based on the maximum amount of continuum dereddening which can be applied without giving the big blue bump a complex shape. For six out of the seven quasars, we find that the intrinsic E(B-V) < 0.03, and the seventh QSO requires intrinsic E(B-V) < 0.045. We briefly discuss some of the implications of the derived intrinsic continuum reddening limits. We use geometrically thin accretion disk models to derive the black hole masses and accretion rates implied by the spectral energy distributions. Even if we neglect intrinsic reddening, we find that a large fraction of the quasars require super-Eddington accretion rates (which is not consistent with the thin disk assumption). Comparison of the data in this paper to a large body of data from the literature on the accretion disk MBH -Ṁ grid calculated by Wandel & Petrosian reveals that our quasars are among the brightest in the sky at 1450 Å, and ostensibly suggests that the fraction of quasars which require super-Eddington accretion rates is much smaller than the fraction that we derive from our data alone. However, intrinsic continuum reddening has been ignored in this comparison, and a small amount of intrinsic reddening will push more of the quasars into the super-Eddington regime. We also plot the recent reverberation monitoring results on NGC 5548 and NGC 3783 on the Wandel & Petrosian grid, and we find that these Seyfert galaxies appear to vary along lines of constant MBH. Continuum flux from two of the quasars in our main sample, PG 1338+416 and PG 1630+377, is detected at λrest < 584 Å. These quasars can in principle be used for the He éGunn-Peterson test, but the S/N of IUE spectra of individual objects is usually too low to place interesting limits on the Gunn-Peterson optical depth. In order to improve the S/N, we have formed a composite spectrum from the spectra of five quasars detected with IUE at λrest < 584 Å, and we have used this composite spectrum to place a tighter limit on τGP,He I. From the composite spectrum we find that at = 1.58, τGP,He I ≤ 0.09 at the 3 σ level. We briefly discuss intermediate-redshift Lyman limit systems (0.5 ≤ zLL ≤ 1.6) detected in the IUE spectra of five quasars, including lower limits on N(H I) in each Lyman limit system.
- Aldcroft, T. L., Elvis, M., & Bechtold, J. (1993). A sample of lobe-dominated quasars with Mg II absorption lines. Astronomical Journal, 105(6), 2054-2063.More infoAbstract: We present a sample of quasars which are lobe-dominated in their radio emission and contain Mg II absorption line systems. This sample will be useful in a search for redshifted H I 21 cm absorbers which are along lines of sight different from the optical. These systems will allow the measurement of the linear size and related physical parameters of the absorption line clouds. Since quasars appropriate for this study are rare, building this sample requires a substantial database of radio and optical observations. We have defined a set of criteria for selecting these objects and obtained the necessary data, from the literature and from new optical and Very Large Array (VLA) observations, to assemble a sample based on these criteria. Out of 4234 Quasi Stellar Objects (QSOs), we find 31 lobe-dominated quasars which are appropriate for optical and radio absorption line study in the Northern hemisphere. We have obtained or located optical spectra for 29 of these 31 quasars. In the optical spectra we find 17 Mg II absorption systems, with redshifts between 0.3 and 1.4 and Mg II λ2796 rest equivalent widths between 0.3 and 2.0 Å. Based on statistics of 21 cm absorption in Mg II selected QSOs we expect this sample of 17 systems to yield one or two new H I absorbers. In this paper we give an analysis of our criteria, discuss the sample, and present new VLA observations of 16 quasars.
- Dietrich, M., Kollatschny, W., Peterson, B. M., Bechtold, J., Bertram, R., Bochkarev, N. G., Boroson, T. A., Carone, T. E., Elvis, M., Filippenko, A. V., Gaskell, C. M., Huchra, J. P., Hutchings, J. B., Koratkar, A. P., Korista, K. T., Lame, N. J., Laor, A., MacAlpine, G. M., Malkan, M. A., , Mendes, C., et al. (1993). Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. IV. Intensity variations of the optical emission lines of NGC 5548. Astrophysical Journal Letters, 408(2), 416-427.More infoAbstract: We present measurements of optical emission-line flux variations based on spectra of the Seyfert galaxy NGC 5548 obtained between 1988 December and 1989 October during the course of a large-scale international monitoring effort. The data presented here supplement previously published measurements of the UV lines and continuum, optical continuum, and broad Hβ emission line. All of the measured optical emission lines, Hα, Hβ, Hγ, He I λ5876, and He II λ4686, show the same qualitative behavior as the UV and optical continua, but with short time delays, or lags, which are different for the various lines. We apply cross-correlation analysis to measure the lags between the various lines and the continuum. We find similar lags with respect to the UV continuum for Hα and Hβ, 17 and 19 days, respectively. The lag for Hγ is shorter (13 days), only somewhat larger than the lag measured for Lyα (about 10 days). The helium lines respond to continuum variations more rapidly than the hydrogen lines, with lags of about 7 days for He λ4686 and 11 days for He I λ5876.
- Maoz, D., Netzer, H., Peterson, B. M., Bechtold, J., Bertram, R., Bochkarev, N. G., Carone, T. E., Dietrich, M., Filippenko, A. V., Kollatschny, W., Korista, K. T., Shapovalova, A. I., Shields, J. C., Smith, P. S., Thiele, U., & Wagner, R. M. (1993). Variations of the ultraviolet Fe II and balmer continuum emission in the seyfert galaxy NGC 5548. Astrophysical Journal Letters, 404(2), 576-583.More infoAbstract: We present measurements of the Balmer continuum/Fe II emission blend (the "small blue bump") between 2160 and 4130 Å in the Seyfert galaxy NGC 5548. The measurements are from spectra obtained as part of the combined space-based and ground-based monitoring program of this object in 1988-1989. An iterative scheme is used to determine and subtract the continuum emission underlying the emission blend so as to obtain a light curve sampled once every 4 days. The small blue bump is an important component of the emission-line cooling, constituting about one third of the line flux in this object. Its flux varies with an amplitude of approximately ±20% about the mean, similar to the amplitude of the Balmer line variations during the same period. Its light curve resembles that of Lyα, with a lag of ∼10 days behind the continuum variations The bump variation amplitude is independent of the wavelength interval where it is measured, which indicates that both the Balmer continuum and Fe II emission have comparable variation amplitudes. These results suggest that the Fe II UV multiplets and the Balmer continuum are emitted in the same parts of the broad-line region as most other broad emission lines in this object.
- Saffer, R. A., Wade, R. A., Liebert, J., Green, R. F., Sion, E. M., Bechtold, J., Foss, D., & Kidder, K. (1993). PG 0308+096 and PG 1026+002: Two new short period binary stars resulting from common-envelope evolution. Astronomical Journal, 105(5), 1945-1955.More infoAbstract: We have studied the ultraviolet excess stars PG 0308+096 and PG 1026+002 by means of ultraviolet and optical spectroscopy and spectrophotometry. Both objects have been found to be short-period detached binary systems, consisting of DA white dwarfs and dMe main-sequence companions, and can be understood as the result of prior common-envelope binary evolution. Both systems show strong Ha emission periodically modulated in radial velocity. PG 0308+096 consists of a DA 2 white dwarf (Teff=26 200±2000 K, log g=7.5±0.4) and a M4.5e main-sequence secondary. The orbital period is P=0.284 309±0.000 021 day with an additional error due to cycle count ambiguity of ±0.002 365 day. Spectroscopic estimates for the masses of the white dwarf and M dwarf are, respectively, script M sign1=0.39+0.13-0.10 script M sign⊙ and script M sign2=0.18±0.05 script M sign⊙. The corresponding inferred range on orbital inclination is i=42°±9°, or i=46°± 10° if the observed radial velocity semiamplitude of the M dwarf, K2, is corrected for bias. PG 0308+096 shows periodic modulations of Hα emission equivalent width, with a minimum occurring when the M dwarf is at inferior conjunction. If the equivalent width variations are due to reprocessing of the EUV flux from the hot primary in the chromosphere of the secondary, the inclination of the orbital plane to the line of sight is close to 30°; if a portion of the Hα emission is "intrinsic" chromospheric activity on the late-type star, uniform over stellar longitude, the inclination is higher. PG 1026+002 consists of a DA 3 white dwarf (Teff= 17 600±2000 K, log g=8.1±0.4) and a M4e main-sequence secondary. Its orbital period is P=0.597 257 0±0.000 004 9 day with no cycle count ambiguity. Spectroscopic mass estimates are script M sign1=0.65+0.26-0.21 script M sign⊙ and script M sign2=0.22±0.05 script M sign⊙, corresponding to an inclination bounded at i > 49°, or i > 51° if K2 is corrected for bias. Equivalent width variations in Hα emission also are seen for PG 1026+002, but because the primary is cooler this cannot be attributed to reprocessing of EUV photons. Stellar activity is thus the favored explanation for the Hα emission, although in this picture there are not be a natural explanation for the phase dependence of the equivalent width variations. These estimates for the stellar and orbital parameters for PG 0308+096 and PG 1026+002 suggest that the orbits will evolve by angular momentum loss through gravitational wave radiation to semidetached configurations in 1010 and 1011 yr, respectively. These times would each be reduced by a factor of 10 if angular momentum loss due to magnetic braking is significant.
- Bechtold, J., & Ellingson, E. (1992). Mg II absorption by previously known galaxies at z ≈ 0.5. Astrophysical Journal Letters, 396(1), 20-34.More infoAbstract: We have obtained spectra at the Multiple Mirror Telescope of nine QSOs in order to search for Mg II λλ2796, 2803 absorption from intervening galaxies with previously determined redshifts between 0.2 and 0.7. We have detected two Mg II systems with the redshift of known galaxies, including one associated with a cluster of galaxies at z = 0.362. From the lack of detectable Mg II absorption for a large number of other galaxies, we conclude that the galaxies that do absorb must have an effective cross section for absorption at least twice as large in radius as previously thought, in order to account for Mg II absorber statistics. Contrary to previous work, we find that the galaxies with detectable absorption have the same distribution of absolute luminosities as galaxies which show no absorption.
- Rauch, M., Carswell, R. F., Chaffee, F. H., Foltz, C. B., Webb, J. K., Weymann, R. J., Bechtold, J., & Green, R. F. (1992). The lyman forest of 0014+813. Astrophysical Journal Letters, 390(2), 387-404.More infoAbstract: The results of 23 km s-1 resolution echelle spectroscopy of the Lyman forest region of the z = 3.38 QSO 0014+813 are described. Voigt profile fits to the Lyman series absorption lines yield H I column density and Doppler parameter distributions similar to those obtained in three previous studies of other objects. There is no evidence so far of significant changes of the behavior of these distributions with redshift, except for the number of systems per unit redshift which, for log N(H I) > 13.75 (cgs), is proportional to (1 + z)2.1 ± 0.5. We find no evidence for a correlation between the Doppler parameter and column density and show that an apparent correlation is due entirely to selection effects of line detection and fitting. While the Lyman forest systems as a whole show no clustering, there appears to be a population of weak, narrow-lined systems which show clustering on scales of ≲1000 km s-1. It is not clear if these are unidentified heavy element lines or a genuine Lyman forest component. A simple test for voids along the sight line to 0014+813 proved negative. However, applying the same test to the spectrum of 0420-388 reveals a 24 Mpc region where the line number density is significantly below the mean. The depletion is unlikely to be due to a single nearby ionization source.
- Dobrzycki, A., & Bechtold, J. (1991). A ∼10 Mpc void in the Lyα forest at z = 3.17. Astrophysical Journal Letters, 377(2 PART 2), L69-L72.More infoAbstract: The spectrum of the z = 3.285 quasar, Q0302-003, shows a large (∼10 Mpc) void in the Lyα forest at z ≈ 3.17. By simulating the absorption spectrum of the quasar with a range of Lyα forest cloud parameters, we find that the probability of such a void occurring by chance is ∼2 × 10-4. Since the void is near (although not centered on) the redshift of a bright foreground quasar, we discuss the possibility that the void results from ionization of the clouds by the EUV radiation of this QSO.
- Pei, Y. C., Fall, S. M., & Bechtold, J. (1991). Confirmation of dust in damped lyman-alpha systems. Astrophysical Journal Letters, 378(1), 6-16.More infoAbstract: As part of a search for dust at high redshifts, we have acquired new spectra of quasars in the Wolfe et al. sample: 13 with damped Lya systems along the lines of sight and 15 without. Our spectra cover the region 3950-6900 Å at a resolution of 15 Å with signal-to-noise ratios of 10-50. We have determined spectral indices over a common range of wavelengths in the rest frames of the quasars between Lyα and C IV emission. Several internal and external checks indicate that the typical errors in the spectral indices are ±0.1. We find that quasars with damped Lyα systems in the foreground are stochastically redder than those without damped Lya systems in the foreground. This difference, significant at the 3 σ level, confirms our previous detection in the sample of Sargent, Steidel, & Boksenberg. Combining the Wolfe et al. and Sargent et al. samples increases the significance of the reddening to at least 4 σ. We compute dust-to-gas ratios from the spectral indices on the assumption that the extinction curve in the damped Lyα systems has the same shape as that in the Milky Way or the Large or Small Magellanic Cloud. Galactic-type dust appears to be ruled out by the absence of strong extinction near 2175 Å in the rest frames of several damped Lyα systems. Our best estimates of the typical dust-to-gas ratio in the damped Lyα systems are then 5%-20% of that in the Milky Way. This result, together with recent measurements of the gas-phase abundances of Zn and Cr in three damped Lyα systems, indicates that the overall abundances of heavy elements (in both the gas and solid phases) are about one order of magnitude lower than the Galactic value.
- Peterson, B. M., Balonek, T. J., Barker, E. S., Bechtold, J., Bertram, R., Bochkarev, N. G., Bolte, M. J., Bond, D., Boroson, T. A., Carini, M. T., Carone, T. E., Christensen, J. A., Clements, S. D., Cochran, A. L., Cohen, R. D., Crampton, D., Dietrich, M., Elvis, M., Ferguson, A., , Filippenko, A. V., et al. (1991). Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. II. An intensive study of NGC 5548 at optical wavelengths. Astrophysical Journal Letters, 368(1), 119-137.More infoAbstract: We report on a large, international program of ground-based optical spectroscopy and photometry of the variable Seyfert 1 galaxy NGC 5548 undertaken in support of an IUE monitoring campaign described by Clavel and coworkers. In this contribution, we present the data base and describe the methods used to correct for systematic differences between spectra from different sources. Optical continuum and Hβ emission-line light curves are derived from the spectra. The behavior of the optical continuum is qualitatively the same as the behavior of the ultraviolet continuum. Cross-correlation of the ultraviolet and optical continuum measurements does not reveal any significant lag between them. The Hβ emission-line variations show the same basic pattern as seen in the continuum and ultraviolet emission lines, with Hβ lagging behind the continuum by ∼20 days. This is significantly larger than the ∼10 day lag deduced for Lyα.
- Tripp, T. M., Green, R. F., & Bechtold, J. (1990). IUE observations of PG 1115 + 080: The He I Gunn-Peterson test and a search for the lensing galaxy. Astrophysical Journal, 364(2 PART 2), L29-L32.More infoAbstract: We have obtained new IUE observations of PG 1115+080 (zem = 1.722), the "triple quasar," in order to carry out the He I Gunn-Peterson test with greater sensitivity and to search for a Lyman-limit discontinuity which could reveal the redshift of the gravitational lens. We find that nHeI(z = 1.722) ≤ 7 × 10-11h100 cm-3 at the 3 σ level. We have used this density to set a curve of constraint in the log TIGM-log nHe plane according to the shock-heated and photoionized IGM models. The predominantly shock-heated IGM model requires that TIGM ≥ 105.3 K. If the IGM is both photoionized by the standard QSO diffuse radiation field and shock-heated, then the limits on hydrogen Lyman-alpha provide more stringent limits on the density and temperature of the IGM. We have found no evidence of the gravitational lens, placing an upper limit on NH of 3 × 1016 cm-2 for zlens ≳ 0.39.
- Thibodeau, C., Rafiee, A., Scott, J. E., Richmond, M., Benigno, G., Kubli, A., Bechtold, J., & Ellingson, E. (2013, jan). Associated Absorption in Low Redshift Quasar Environments. In American Astronomical Society Meeting Abstracts, 221, #339.32.
- Croft, R. A., Arnau, E., Aubourg, E., Bailey, S., Bechtold, J., Bhardwaj, V., Bolton, A., Borde, A., Brinkmann, J., Busca, N., Carithers, W., Cen, R., Charlassier, R., Cortes, M., Dall'Aglio, A., Cristiani, S., Dawson, K., Delubac, T., Font-Ribera, A., , Hamilton, J., et al. (2012, jan). Dense Sampling and Large Volume: The Structure of the Intergalactic Medium from 50,000 SDSS3 BOSS Quasar Absorption Spectra. In American Astronomical Society Meeting Abstracts #219, 219, #324.03.