UC Irvine

In this thesis, I present two projects addressing two problems in galaxy evolution: the nature of star-formation in high-z galaxies and the origin of Ultra-Diffuse Galaxies.

First, I investigate the relationship between the CO-H2 conversion factor (αCO) and surface density in z ∼ 1 Milky Way-like galaxies. In this work, I demonstrate that the correlation between αCO and surface density is sensitive to the state of molecular gas within massive galaxies. By inferring αCO values for a large sample of galaxies at z ∼ 0 and z ∼ 1 from the observed star formation rate and the CO luminosity, I show that molecular gas conditions and the process of star formation in typical high-z systems is similar to low-z counterparts. The increased star-formation rates among high-z galaxies are thus primarily due to an increased supply of molecular gas in high-z systems.

Secondly, I present a model for the formation of Ultra-Diffuse Galaxies (UDGs) through tidal stripping and heating. This model builds upon results from high-resolution simulations, which have demonstrated that changes to the stellar mass and half-light radii of satellites in response to tidal stripping can be determined remarkably well using only knowledge of the subhalo orbit and initial properties of the satellite. This relatively simple model is able to reproduce many of the observed properties of UDGs, including the stellar mass and size distributions, as well as the observed abundance within ∼ 10%.