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 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 \gtrsim 0.01 ~ { } L* or stellar mass M _ { * } \gtrsim 10 ^ { 8 } ~ { } M _ { \odot } .
We report two principal findings .
First , for galaxies with impact parameter \rho < 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 _ { \odot } ; lower mass galaxies rarely exhibit significant C iv absorption ( covering fraction f _ { C } = 9 ^ { +12 } _ { -6 } \% for 11 galaxies with M _ { * } < 10 ^ { 9.5 } ~ { } M _ { \odot } ) .
Second , C iv detection within the M _ { * } > 10 ^ { 9.5 } ~ { } M _ { \odot } population depends on environment .
Using a fixed-aperture environmental density metric for galaxies with \rho < 160 kpc at z < 0.055 , we find that 57 ^ { +12 } _ { -13 } % ( 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 _ { \odot } .
In contrast to C iv , H i is pervasive in the CGM without regard to mass or environment .
These results indicate that C iv absorbers with log N ( { \text { C } } ~ { } \textsc { iv } ) \gtrsim 13.5 ~ { } { cm } ^ { -2 } trace the halos of M _ { * } > 10 ^ { 9.5 } ~ { } M _ { \odot } galaxies but also reflect larger scale environmental conditions .