Colloquia
Tracking the Evolution of Strong, 1.5 < z < 4.5 CIV Absorbers with Thousands of Systems
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 1.5 < z < 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 1.5 < z < 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 0 < z < 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 other unexpected discoveries.[Back]