Astronomy Tea Talk

Spectroscopic surveys of quasars yield a random sample of intervening absorbing gas clouds that can be used to constrain the on-going and summative enrichment processes in the universe. The CIV doublet has proven to be an important tracer of the IGM and its evolution from z = 6 to 0. This transition has been well-studied at high redshift because: it is a strong transition of a common metal; it is observable outside the Ly-alpha forest, where it becomes easier to identify; it redshifts into optical passbands for z=1.5-4.5; and it is a resonant doublet, which gives it distinctive characteristics that enable surveys to be largely automated. We have vastly improved the z=1.5-4.5 absorber measurements by identifying over 15,000 CIV systems from a survey of thousands of SDSS DR7 QSOs. No longer dominated by Poisson errors, the CIV redshift (non)evolution stands out clearly. For example, the shape of the CIV distribution has not evolved over the 3 Gyr span of the sample, but there has been a two-fold increase in the CIV number density (detected at > 30 sigma). Since the strong CIV absorbers detectable in SDSS spectra likely arise in the extended gaseous halos of galaxies, we can show that the change in the number density is probably largely driven by the change in the number of galaxies. We also constructed a uniform z=0-0.6 dataset by combining the SDSS survey with the z < 1 HST results (Cooksey et al. 2010) and the new z > 5 FIRE results (Simcoe et al. 2011). Thus, we can compare apples-to-apples: the absorber density over time and the CIV mass density evolution. This is the first in a series on our surveys for various metal-line absorption systems in SDSS DR7 QSOs, and we share some early results of the upcoming papers.