Identifying Circumgalactic Medium Absorption in QSO Spectra: A Bayesian
  Approach
  We present a study of candidate galaxy-absorber pairs for 43 low redshift QSO
sightlines ($0.06 < z < 0.85$) observed with the {\it Hubble Space
Telescope}/Cosmic Origins Spectrograph that lie within the footprint of the
Sloan Digital Sky Survey with a statistical approach to match absorbers with
galaxies near the QSO lines of sight using only the SDSS Data Release 12
photometric data for the galaxies, including estimates of their redshifts. Our
Bayesian methods combine the SDSS photometric information with measured
properties of the circumgalactic medium to find the most probable galaxy match,
if any, for each absorber in the line of sight QSO spectrum. We find $\sim$630
candidate galaxy-absorber pairs using two different statistics. The methods are
able to reproduce pairs reported in the targeted spectroscopic studies upon
which we base the statistics at a rate of 72\%. The properties of the galaxies
comprising the candidate pairs have median redshift, luminosity, and stellar
mass, all estimated from the photometric data, $z=0.13$, $L=0.1L^*$, and
$\log(M_*/M_{Sun}) = 9.7$. The median impact parameter of the candidate pairs
is $\sim$430~kpc, or $\sim 3.5$ times the galaxy virial radius. The results are
broadly consistent with the high \lya\ covering fraction out to this radius
found in previous studies. This method of matching absorbers and galaxies can
be used to prioritize targets for spectroscopic studies, and we present
specific examples of promising systems for such follow-up.
