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 ({cz} ≤slant 10,000 {km} {{{s}}}^-1), using archival Cosmic Origins Spectrograph spectra of background quasi-stellar objects. This initial sample contains 33 sightlines chosen for their proximity to large galaxies (D≥slant 25 kpc) and high signal-to-noise ratios (S/N ≥slant 10), yielding 48 Lyα 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 Lyα equivalent width (EW) and impact parameter (ρ) when we normalize by galaxy virial radius (R _vir). Galaxies associated with a Lyα absorber are found to be more highly inclined than galaxies in the survey volume at a > 99 % confidence level (equivalent to ∼ 3.6σ 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 Lyα.