Year: 2010
Type: article
Abstract: ABSTRACT We perform a semi-automated survey for τ912 ⩾ 2 Lyman limit systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey, Data Release 7. From a starting sample of 2473 quasars with z em = 3.6–5.0, we analyze 429 spectra meeting strict selection criteria for a total redshift path Δz = 93.8 and identify 190 intervening systems at z LLS ⩾ 3.3. The incidence of τ912 ⩾ 2 LLSs per unit redshift, ℓτ⩾2(z), is well described by a single power law at these redshifts: , with z * ≡ 3.7, C LLS = 1.9 ± 0.2, and γLLS = 5.1 ± 1.5 (68% c.l.). These values are systematically lower than previous estimates (especially at z < 4) but are consistent with recent measurements of the mean free path to ionizing radiation. Extrapolations of this power law to z = 0 are inconsistent with previous estimations of ℓ(z) at z < 1 and may indicate a break at z ≈ 2, similar to that observed for the Lyα forest. Our results also indicate that the systems giving rise to LLS absorption decrease by ≈50% in comoving number density and/or physical size from z = 4 to 3.3, perhaps due to an enhanced extragalactic ultraviolet background. The observations place an integral constraint on the H i frequency distribution f(N H i , X) and indicate that the power-law slope is likely shallower than β = −1 at . Including other constraints on f(N H i , X) from the literature, we infer that β is steeper than β = −1.7 at , implying at least two inflections in f(N H i , X). We also perform a survey for proximate LLSs (PLLSs) and find that ℓPLLS(z) is systematically lower (≈25%) than intervening systems. Finally, we estimate that systematic effects impose an uncertainty of 10%–20% in the ℓ(z) measurements; these effects may limit the precision of all future surveys.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Funders: National Science Foundation, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, W. M. Keck Foundation, Princeton University, Ohio State University, California Institute of Technology, University of Washington, Johns Hopkins University, University of Pittsburgh, Case Western Reserve University, Drexel University, Universität Basel, University of Portsmouth, New Mexico State University, Chinese Academy of Sciences, Max-Planck-Gesellschaft, Max-Planck-Institut für Astronomie, U.S. Naval Observatory, Fermilab, Los Alamos National Laboratory
OpenAlex ID: W2099603107