A DEEP SEARCH FOR FAINT GALAXIES ASSOCIATED WITH VERY LOW REDSHIFT C iv ABSORBERS. III. THE MASS- AND ENVIRONMENT-DEPENDENT CIRCUMGALACTIC MEDIUM

ABSTRACT Using Hubble Space Telescope Cosmic Origins Spectrograph observations of 89 QSO sightlines through the Sloan Digital Sky Survey footprint, we study the relationships between C iv absorption systems and the properties of nearby galaxies, as well as the large-scale environment. To maintain sensitivity to very faint galaxies, we restrict our sample to , which defines a complete galaxy survey to or stellar mass . We report two principal findings. First, for galaxies with impact parameter , C iv detection strongly depends on the luminosity/stellar mass of the nearby galaxy. C iv is preferentially associated with galaxies with lower-mass galaxies rarely exhibit significant C iv absorption (covering fraction for 11 galaxies with ). Second, C iv detection within the population depends on environment. Using a fixed-aperture environmental density metric for galaxies with ρ < 160 kpc at , we find that (8/14) of galaxies in low-density regions (regions with fewer than seven galaxies within 1.5 Mpc) have affiliated C iv absorption; however, none (0/7) of the galaxies in denser regions show C iv . Similarly, the C iv detection rate is lower for galaxies residing in groups with dark matter halo masses of . In contrast to C iv , H i is pervasive in the circumgalactic medium without regard to mass or environment. These results indicate that C iv absorbers with trace the halos of galaxies but also reflect larger-scale environmental conditions.