A Deep Search For Faint Galaxies Associated With Very Low-redshift C IV
  Absorbers: II. Program Design, Absorption-line Measurements, and Absorber
  Statistics
  To investigate the evolution of metal-enriched gas over recent cosmic epochs
as well as to characterize the diffuse, ionized, metal-enriched circumgalactic
medium (CGM), we have conducted a blind survey for C IV absorption systems in
89 QSO sightlines observed with the Hubble Space Telescope (HST) Cosmic Origins
Spectrograph (COS). We have identified 42 absorbers at z < 0.16, comprising the
largest uniform blind sample size to date in this redshift range. Our
measurements indicate an increasing C IV absorber number density per comoving
path length (dN/dX = 7.5 +/- 1.1) and modestly increasing mass density relative
to the critical density of the Universe (Omega(C IV) = 10.0 +/- 1.5 x 10^-8 )
from z ~ 1.5 to the present epoch, consistent with predictions from
cosmological hydrodynamical simulations. Furthermore, the data support a
functional form for the column density distribution function that deviates from
a single power-law, also consistent with independent theoretical predictions.
As the data also probe heavy element ions in addition to C IV at the same
redshifts, we identify, measure, and search for correlations between column
densities of these species where components appear aligned in velocity. Among
these ion-ion correlations, we find evidence for tight correlations between C
II and Si II, C II and Si III, and C IV and Si IV, suggesting that these pairs
of species arise in similar ionization conditions. However, the evidence for
correlations decreases as the difference in ionization potential increases.
Finally, when controlling for observational bias, we find only marginal
evidence for a correlation (86.8% likelihood) between the Doppler line width
b(C IV) and column density N(C IV).
