*Updated:* 14 Mar 2016

**Reference:** Cooksey et al. (2013,
ApJ, 763, 37:
online,
PDF)

**Notice:** 14 March 2016—Updated
catalog available.

**Abstract:**
We have vastly increased the C IV statistics at
intermediate redshift by surveying the thousands of QSOs in the
Sloan Digital Sky Survey Data-Release 7. We visually verified over
16,000 C IV systems with 1.46 < *z* <
4.55—a sample size that renders Poisson error negligible.
Detailed Monte Carlo simulations show we are approximately 50%
complete down to rest equivalent widths *W*_{r} ≈
0.6 Å. We analyzed the sample as a whole and in ten small
redshift bins with approximately 1500 doublets each. The equivalent
width frequency distributions ƒ(*W*_{r}) were well
modeled by an exponential, with little evolution in shape. In
contrast with previous studies that modeled the frequency
distribution as a single power law, the fitted exponential gives a
finite mass density for C IV ions. The
co-moving line density
*dN*_{C IV}/*dX* evolved
smoothly with redshift, increasing by about a factor of 2.37
± 0.09 from *z* = 4.55 to 1.96, then plateauing at
*dN*_{C IV}/*dX* ≈
0.34 for *z* = 1.96 to 1.46. Comparing our SDSS sample with
*z* < 1 (ultraviolet) and *z* > 5 (infrared) surveys, we
see an approximately ten-fold increase in
*dN*_{C IV}/*dX* over
*z* ≈ 6 → 0, for *W*_{r} ≥ 0.6
Å. This suggests a monotonic and significant increase in the
enrichment of gas outside galaxies over the 12 Gyr lifetime of the
universe.

**Reference:** Seyffert et al. (2013,
ApJ, 779, 161:
online,
PDF)

**Abstract:**
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 was divided into 14 small redshift bins with roughly 2,500
doublets in each, and from Monte-Carlo simulations, we estimate 50%
completeness at rest equivalent width *W*_{r} ≈
0.8 Å. The equivalent-width frequency distribution is
described well by an exponential model for 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 extremely 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 *W*_{r} ≥ 1 Å absorber line density
grew, *dN*_{Mg II}/*dX*, by
roughly 45%. Finally, we explore the different evolution of various
absorber populations—damped Lyman-$\alpha$ absorbers,
Lyman-limit systems, strong C IV absorbers,
and strong and weaker Mg II
systems—across cosmic time (0 < *z* < 6).