Quasars Probing Quasars. I. Optically Thick Absorbers near Luminous Quasars

By J. Hennawi, J. Xavier Prochaska, S. Burles, M. Strauss, Gordon Richards, David Schlegel, Xiaohui Fan, D. Schneider, N. Zakamska, M. Oguri and 3 more. 2006

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With close pairs of quasars at different redshifts, a background quasar sight line can be used to study a foreground quasar's environment in absorption. We search 149 moderate-resolution background quasar spectra from Gemini, Keck, the MMT, and the SDSS to survey Lyman limit systems (LLSs) and damped Lyα systems (DLAs) in the vicinity of 1.8 < z < 4.0 luminous foreground quasars. A sample of 27 new quasar-absorber pairs is uncovered with column densities 1017.2 cm-2 < N < 1020.9 cm-2 and transverse (proper) distances of 22 h-1 kpc < R < 1.7 h-1 Mpc from the foreground quasars. If they emit isotropically, the implied ionizing photon fluxes are a factor of ~5-8000 times larger than the ambient extragalactic UV background over this range of distances. The observed probability of intercepting an absorber is very high for small separations: six out of eight projected sight lines with transverse separations R < 150 h-1 kpc have an absorber coincident with the foreground quasar, of which four have N > 1019 cm-2. The covering factor of N > 1019 cm-2 absorbers is thus ~50% (4/8) on these small scales, whereas ≲2% would have been expected at random. There are many cosmological applications of these new sight lines: they provide laboratories for studying fluorescent Lyα recombination radiation from LLSs; they constrain the environments, emission geometry, and radiative histories of quasars; and they shed light on the physical nature of LLSs and DLAs.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/2401c8cf1e721d1f56b6f3b9beeba99f4883e56d

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Citations in the corpus

Absorption-line systems in simulated galaxies fed by cold streams (2011, background): “Within ∼100 h−1 kpc, the covering factor of absorbers in the transverse direction of quasi-stellar object (QSO) host galaxies is significantly higher than our estimates, being unity for NH I > 1.6 × 1017 cm−2 (Hennawi et al. 2006) and 30 per cent for NH I > 1019 cm−2 (Hennawi & Prochaska 2007).”
Neutral hydrogen in galaxy haloes at the peak of the cosmic star formation history (2014, background): “…of spectroscopic measurements of absorption by hydrogen and metals in the circumgalactic medium (CGM), both at low redshift and around the peak of the star formation history at z & 2 (e.g., Hennawi et al. 2006; Steidel et al. 2010; Tumlinson et al. 2011; Rudie et al. c© 0000 RAS ar X iv :1 40 9.”
A High-Resolution Survey of Low-Redshift QSO Absorption Lines: Statistics and Physical Conditions of O VI Absorbers (2007, background): “Finally, thanks to the huge number of quasars discovered by large-scale surveys such as SDSS, it has become possible use background QSOs to probe absorption from gas affiliated with a foreground, lower-redshift QSO (Bowen et al. 2006; Hennawi et al. 2006).”
A Direct Precision Measurement of the Intergalactic Lyα Opacity at 2 ≤ z ≤ 4.2 (2007, background): “…to account for the large typical uncertainties in quasar redshift determinations (for related discussions on quasar redshift uncertainties, see e.g., Gaskell 1982; Tytler & Fan 1992; Vanden Berk et al. 2001; Richards et al. 2002; Hennawi et al. 2006; Shen et al. 2007; Faucher-Giguere et al. 2007).”
Clustering of High-Redshift (z ≥ 2.9) Quasars from the Sloan Digital Sky Survey (2007, methodology): “Our sample cannot explore clustering below ∼ 1 h−1 Mpc because of fiber collisions; we are extending the methods of Hennawi et al. (2006a) to find close pairs of high-redshift quasars, to determine whether the excess clutering found at moderate redshift extends toz> 3.”
The clustering of intermediate-redshift quasars as measured by the Baryon Oscillation Spectroscopic Survey (2012, methodology): “…recently included enough objects to study their clustering with some precision (Porciani, Magliocchetti & Norberg 2004; Croom et al. 2005; Porciani & Norberg 2006; Hennawi et al. 2006a; Myers et al. 2006, 2007a,b; da Angela et al. 2008; Padmanabhan et al. 2009; Ross et al. 2009; Shen et al. 2009).”
Evolution of the Intergalactic Opacity: Implications for the Ionizing Background, Cosmic Star Formation, and Quasar Activity (2008, background): “…effect used quasar systemic redshifts based on broad emission lines, which are increasingly recognized as biased measures as a result of inflows and outflows of material (Gaskell 1982; Tytler & Fan 1992; Vanden Berk et al. 2001; Richards et al. 2002; Hennawi et al. 2006; Hennawi & Prochaska 2007).”