Using Metals and Stars to Constrain Galaxies' Past Gaseous Inflows and Outflows

Abstract

As galaxies evolve, they must enrich and exchange gas with the surrounding medium, but the timing of these processes and how much gas is involved remain poorly constrained by observations. In this thesis, I use observations of the metal content of galaxies to place constraints on the history of gas inflow and outflow processes in the local universe. First, I use a large galaxy sample to study the relationship between stellar mass (M*), gas-phase metallicity (Z), and star formation rate, which is thought to encode the strength and duration of metal dilution events due to inflows of metal-poor gas and/or metal-enriched outflows. I find that possible biases in inferred galaxy properties, particularly M* and Z, can alter the apparent strength of the correlation, and therefore its physical interpretation. I then use high-quality, spatially resolved measurements of star formation history (SFH) and dust content and geometry in the nearby galaxy M31 to test standard methods of inferring M*, and demonstrate that both recent star formation and variation in star-dust geometry can bias the M* inferred from state-of-the-art models. Finally, I use the same SFHs to calculate the history of metal production in M31, and compare to a census of its present-day metal content to show that M31 has lost metal mass in gaseous outflows over its lifetime, even after accounting for systematic uncertainties. I calculate the implied metallicity of the circumgalactic medium and average mass outflow rate from M31, and show that metals have been redistributed out of the central disk during the last ~1.5 Gyr.