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Description
We have performed an analysis of over 34000 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 W_r_{approx}0.8{AA}. 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 reveals 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 came by their different results, which qualitatively agree but because of the very small uncertainties, differ by a statistically significant amount. The estimated physical cross section of Mg II-absorbing galaxy halos increased approximately threefold from z=0.4 to z=2.3, while the W_r_>=1{AA} absorber line density, dN_MgII_/dX, grew by roughly 45%. Finally, we explore the different evolution of various absorber populations --damped Ly{alpha} absorbers, Lyman limit systems, strong C IV absorbers, and strong and weaker MgII systems -- across cosmic time (0<z<6).
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