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 0.0015\lt z\lt 0.015, which defines a complete galaxy survey to L≳ 0.01 L\ast or stellar mass {M}_* ≳ {10}⁸ {M}_⊙ . We report two principal findings. First, for galaxies with impact parameter ρ \lt 1 {r}_{vir}, C IV detection strongly depends on the luminosity/stellar mass of the nearby galaxy. C IV is preferentially associated with galaxies with {M}_* \gt {10}^9.5 {M}_⊙ ; lower-mass galaxies rarely exhibit significant C IV absorption (covering fraction {f}_C={9}_-6⁺¹² % for 11 galaxies with {M}_* \lt {10}^9.5 {M}_⊙ ). Second, C IV detection within the {M}_* \gt {10}^9.5 {M}_⊙ population depends on environment. Using a fixed-aperture environmental density metric for galaxies with ρ < 160 kpc at z\lt 0.055, we find that {57}_-13⁺¹² % (8/14) of galaxies in low-density regions (regions with fewer than seven L\gt 0.15 L\ast 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 {M}_{halo}\gt {10}^12.5 {M}_⊙ . 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 {log} N({{C}} {{IV}})≳ 13.5 {{cm}}^-2 trace the halos of {M}_* \gt {10}^9.5 {M}_⊙ galaxies but also reflect larger-scale environmental conditions.