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 < z < 0.015, which defines a complete galaxy survey to L ≳ 0.01 L* or stellar mass M*≳ 10⁸M [subscript ⊙]. We report two principal findings. First, for galaxies with impact parameter ρ < 1r[subscript vir], C IV detection strongly depends on the luminosity/stellar mass of the nearby galaxy. C IV is preferentially associated with galaxies with M[subscript *] > 10 [superscript 9.5] M [subscript ⊙] lower-mass galaxies rarely exhibit significant C IV absorption (covering fraction f [subscript C = 9 [ subscript-6] [subscript +12] % for 11 galaxies with M[subscript *] < 10 [superscript 9.5]M [subscript ⊙]. Second, C IV detection within the M* > 10 [superscript 9.5]M [subscript ⊙] population depends on environment. Using a fixed-aperture environmental density metric for galaxies with ρ < 160 kpc at z < 0.055, we find that 57 [ subscript -13] [superscript +12]% (8/14) of galaxies in low-density regions (regions with fewer than seven L > 0.15L* 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 [subscript halo] > 10[superscript12.5]M [subscript ⊙]. 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 logN(C IV) ≳13.5 [superscript -2 cm] trace the halos of M* > 10 [superscript 9.5]M[subscript ⊙] galaxies but also reflect larger-scale environmental conditions.