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Author ORCID Identifier



Open Access Dissertation

Document Type


Degree Name

Doctor of Philosophy (PhD)

Degree Program


Year Degree Awarded


Month Degree Awarded


First Advisor

Todd M. Tripp

Subject Categories

Cosmology, Relativity, and Gravity | External Galaxies | Stars, Interstellar Medium and the Galaxy


The gaseous halos of galaxies -- the circumgalactic medium (CGM) -- serve as interfaces playing host to the fueling and feedback processes that sustain and regulate star formation. Furthermore, interactions between galaxies one with another and with larger scale structure, such as galaxy cluster halos, must necessarily act through the CGM. This dissertation examines the CGM as traced by H I, C IV, and O VI absorption lines across wide range of halo environments, from isolated dwarf galaxies with M* < 108 Msun to galaxy clusters with Mhalo > 1014 Msun. By first conducting a blind survey of C IV absorption systems in Hubble Space Telescope spectra of quasi-stellar objects, we measure the incidence and cosmic density of triply ionized carbon in the z < 0.16 Universe, showing that both have increased since z~1. We then characterize the associations between C IV absorbers and galaxies leveraging the C IV absorber sample and spectroscopic galaxy surveys with sensitivity down to L ~ 0.01 L* to show a strong dependence of C IV absorption and host galaxy mass, with M* < 109.5 Msun galaxies showing a deficiency of C IV absorption to our detection limits relative to galaxies more massive. However, M* >109.5 Msun galaxies in rich group environments show a suppression in C IV absorption. H I, which is largely ubiquitous in all halos across these scales, is suppressed in the CGM of cluster galaxies. The transformations that occur in the CGM moving from very low-mass halos to very high-mass halos (in dense environments) are consistent with an increasingly hotter CGM as halo mass increases (individual, group, and cluster), where star formation may be quenched by a lack of gas reservoir in the halo or a deprivation of fuel by the hot virialized medium.