2016ApJ...832..124B

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>rsim 0.01 L*or stellar mass M_*>rsim 10⁸ M_☉. We report two principal findings. First, for galaxies with impact parameter ρ< 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_*> 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_*< 10^9.5 M_☉). Second, C iv detection within the M_*> 10^9.5 M_☉ 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_–13⁺¹² % (8/14) of galaxies in low-density regions (regions with fewer than seven L> 0.15 L*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> 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)>rsim 13.5 cm^–2 trace the halos of M_*> 10^9.5 M_☉ galaxies but also reflect larger-scale environmental conditions.