Dwarf Galaxies in the Local Universe as Probes of Stellar and Galactic Evolution

Author: de los Reyes, Mithi Alexa Caballes (Mia)

Year: 2022

Degree: Dissertation (Ph.D.)

Advisor: Kirby, Evan N.

Committee Members: Kasliwal, Mansi M.; Kirby, Evan N.; Hopkins, Philip F.; Steidel, Charles C.; Ravi, Vikram

Option: Astrophysics

DOI: 10.7907/4bz3-2t66

Abstract

Low-mass "dwarf" galaxies are numerous, diverse, and relatively simple, making them excellent laboratories for understanding both stellar and galactic evolution. Dwarf galaxies (galaxies with stellar masses 107-109 solar masses) in the nearby universe (out to distances of ~10 Mpc from our own Milky Way, or redshifts z ≾ 0.01), are a particularly interesting population due to their proximity, which allows us to study them in detail on both spatially-resolved and global scales. In this thesis, I present a variety of observational studies investigating star formation and chemical enrichment within nearby dwarf galaxies.

I first use the chemical abundances of individual stars within Local Group dwarf spheroidal galaxies (dSphs) to understand how past stars lived and died. I use this "galactic archaeology" approach to test theoretical models of Type Ia supernovae by investigating the nucleosynthetic products of these supernovae. For example, using medium-resolution spectra from DEIMOS, I measure manganese abundances that place observational constraints on the masses of Type Ia progenitors. I also describe a novel method to measure the delay-time distribution of Type Ia SNe in an individual dSph, which probes the number of white dwarfs involved in Type Ia SNe. Finally, I show how galactic archaeology can also be used to trace star formation using a simple chemical evolution model.

For more distant galaxies, in which individual stars cannot be resolved, galaxy properties can be measured on larger scales. Using the integral field spectrograph KCWI, I produce spatially-resolved maps of dwarf galaxies located in extremely under-dense regions called cosmic voids. The dynamical properties of these galaxies provide insight into the formation of dwarf galaxies in the absence of large-scale environmental effects. On even larger spatial scales, I use photometry to measure the global properties of galaxies and understand the physical processes that drive star formation on galaxy-wide scales.

These studies pave the way for future work with ongoing and upcoming surveys that will map out our local universe---and the dwarf galaxies around us---in unprecedented detail.

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