Updated: 14 January 2013

Collaborators: Robert Simcoe, Melodie M. Kao (Caltech),
John M. O'Meara, Eduardo Seyffert (MIT), and Jason X. Prochaska

I. Tracking the Evolution of Strong, 1.5 < z < 4.5 C IV Absorbers with Thousands of Systems

Reference: Cooksey et al. (2013, ApJ, 763, 37: online, PDF; also see igmabsorbers.info).

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.