2005/06/28 by David A. Turnshek, Sandhya M. Rao, Turnshek, David A. +7
Physics and Astronomy · #Astrophysics (astro-ph) #FOS: Physical sciences #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0506701
To appear in "Probing Galaxies through Quasar Absorption Lines", Proceedings IAU Colloquium 199, 2005; Williams, Shu, & Menard, eds
arxiv created 2005/06/28 · arxiv updated 2009/12/01
Sloan Digital Sky Survey (SDSS) quasar spectroscopy is yielding a database of strong low-ionization MgII absorbers over the redshift interval 0.36<z<2.28 which is over two orders of magnitude larger than anything previously assembled. HST UV spectroscopy has been used to measure neutral hydrogen column densities for a small subset of them. These data empirically show that MgII absorbers with rest equivalent widths Wλ27960 ≥ 0.6 Åhave a mean neutral hydrogen column density that is roughly constant at N(HI) ≈ 4 × 1020 atoms cm-2, with individual systems lying in the damped Ly-alpha (DLA) and sub-DLA regimes. Since the MgII doublets generally exhibit saturation, the Wλ27960 values are an indication of the absorbers' velocity spreads. Thus, we can study neutral-gas-phase metallicities as a function of kinematics by forming SDSS composite spectra and measuring weak unsaturated metal lines that form in neutral gas (e.g., CrII, FeII, MnII, SiII, ZnII) as a function of Wλ27960. We use this method on SDSS composite spectra to show how metallicity and kinematics are positively correlated for large N(HI) absorbers, including trends related to dust depletion and the enhancement of alpha-elements. We also discuss the need to account for selection effects in DLA surveys, and we make inferences about models for DLA absorption and their contribution to cosmic star formation.