Precious Metals in SDSS Quasar Spectra II: Tracking the Evolution of Strong, 0.4 < z < 2.3 MgII Absorbers with Thousands of Systems

TL;DR

This study analyzes over 34,000 MgII absorption systems in SDSS quasar spectra across redshifts 0.36 to 2.29, revealing evolution in absorber properties and galaxy halo cross-sections over cosmic time.

Contribution

It provides a comprehensive, publicly available catalog of MgII absorbers with detailed analysis of their evolution and comparison with previous surveys, highlighting new insights into absorber populations.

Findings

The equivalent-width distribution becomes flatter with increasing redshift.

The physical cross-section of MgII-absorbing halos increased three-fold from z=0.4 to 2.3.

The line density of strong MgII absorbers grew by roughly 45% over the studied redshift range.

Abstract

We have performed an analysis of over 34,000 MgII 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 W_r ~ 0.8 Angstrom. 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 MgII 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 MgII-absorbing galaxy halos increased three-fold, approximately, from z = 0.4 --> 2.3, while the W_r >= 1 Angstrom absorber line density grew, dN_MgII/dX, by roughly 45%. Finally, we explore the different evolution of various absorber populations - damped Lyman-alpha absorbers, Lyman-limit systems, strong CIV absorbers, and strong and weaker MgII systems - across cosmic time (0 < z < 6).