Probing Large Galaxy Halos at Z ∼ 0 with Automated Lyα-absorption Matching

Abstract

We present initial results from an ongoing large-scale study of the circumgalactic medium in the nearby Universe (  10,000 ), using archival Cosmic Origins Spectrograph spectra of background quasi-stellar objects. This initial sample contains 33 sightlines chosen for their proximity to large galaxies ( kpc) and high signal-to-noise ratios (S/N 10), yielding 48 Ly α absorption lines that we have paired with 33 unique galaxies, with 29 cases where multiple absorbers within a single sightline are paired with the same galaxy. We introduce a likelihood parameter to facilitate the matching of galaxies to absorption lines in a reproducible manner. We find the usual anti-correlation between Ly α equivalent width (EW) and impact parameter ( ρ ) when we normalize by galaxy virial radius ( R vir ). Galaxies associated with a Ly α absorber are found to be more highly inclined than galaxies in the survey volume at a confidence level (equivalent to for a normal distribution). In contrast with suggestions in other recent papers of a correlation with azimuth angle for Mg ii absorption, we find no such correlation for Ly α .