Date of Graduation


Document Type


Degree Type



Eberly College of Arts and Sciences


Physics and Astronomy

Committee Chair

Pisano, D.J.

Committee Co-Chair

McLaughlin, Maura

Committee Member

McLaughlin, Maura

Committee Member

Burke-Spolaor, Sarah

Committee Member

Carignan, Claude


We explore the environment of 36 nearby galaxies in neutral hydrogen (H I) as part of the MeerKAT H I Observations of Nearby Galactic Objects; Observing Southern Emitters (MHONGOOSE) survey with the Robert C. Byrd Green Bank Telescope (GBT), and the Imaging Galaxies Intergalactic and Nearby En- vironment (IMAGINE) survey with the Parkes Radio Telescope. We obtained deep observations of each of these galaxies, reaching column density detection sensitivities as low as NHI ∼ 1e17 cm^−2, which allowed us to quantify the amount of diffuse H I in both samples of galaxies. This allows us to search for evidence of gas that could be accreting onto galaxies via filamentary structures from the cosmic web. These structures are predicted to be low column density gas flows, which should be seen within the dark matter halo of a galaxy.

With our sample of 18 MHONGOOSE galaxies, we are able to make comparisons to environmental factors that are associated with cold accretion. Our GBT observations of diffuse H I in these galaxies do reveal trends in properties associated with this accretion, such as higher amounts of diffuse H I in galaxies with baryonic masses below a threshold of 1e10.3 M⊙. Our data also revealed trends when looking at the dark matter halo masses and rotation velocities of these MHONGOOSE galaxies.

We take a deep look into one of the IMAGINE galaxies, ESO 214-17, revealing a new low column density H I bridge connecting the central galaxy to a companion. We also present a look at the first data sample from the IMAGINE survey with the Parkes telescope. These 18 galaxies were mapped to extremely low H I column densities (NHI ∼ 1e17 cm−2), and extend out to or beyond the virial radius of each galaxy. Encompassing the entire dark matter halo allows us to quantify the amount of HI throughout the halo, and subsequently the circumgalactic medium of each galaxy. Our environmental comparisons with properties associated with cold accretion do not reveal strong trends in the IMAGINE sample, however when combining all 36 galaxies discussed here we do see trends consistent with cold mode accretion. These trends are revealed when we look at baryonic masses, galaxy densities, and to a lesser degree with dark matter halo masses and rotation velocities.