Preprint typeset using LATEX style emulateapj v. 08/22/09 PRECIOUS METALS IN SDSS QUASAR SPECTRA II: TRACKING THE EVOLUTION OF STRONG, 0.4 < Z < 2.3 MG II ABSORBERS WITH THOUSANDS OF SYSTEMS

We have performed an analysis of over 34,000 Mg II doublets at 0.36 < z < 2.29 in Sloan Digital Sky Survey (SDSS) Data-Release 7 quasar spectra; the catalog, advanced data products, and tools for analysis are publicly available. The catalog was divided into 14 small redshift bins with roughly 2500 doublets in each, and from Monte-Carlo simulations, we estimate 50 % completeness at rest equivalent width Wr ≈ 0.8 Å. The equivalent-width frequency distribution is described well by an exponential model at all redshifts, and the distribution becomes flatter with increasing redshift, i.e., there are more strong systems relative to weak ones. Direct comparison with previous SDSS Mg II surveys reveal that we recover at least 70 % of the doublets in these other catalogs, in addition to detecting thousands of new systems. We discuss how these surveys come by their different results, which qualitatively agree but, due to the very small uncertainties, differ by a statistically significant amount. The estimated physical cross-section of Mg II-absorbing galaxy halos increased three-fold, approximately, from z = 0.4 → 2.3, while the Wr ≥ 1 A ̊ absorber line density grew, dNMg II/dX, by roughly 45%. Finally, we explore the different evolution of various absorber populations—damped Lyman-α absorbers, Lyman-limit systems, strong C IV absorbers, and strong and weaker Mg II systems—across cosmic time (0 < z < 6). Subject headings: intergalactic medium – quasars: absorption lines – galaxies: halos — techniques: spectroscopic Online-only material: color figures, machine-readable tables 1