Date of Award

Spring 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Astronomy

First Advisor

Geha, Marla

Abstract

This thesis focuses on low mass, quiescent galaxies in the local universe, with the goal of providing meaningful constraints on the feedback mechanisms that drive quenching in low mass galaxies. We present an in-depth exploration of what may be the lowest mass galaxies still able to self-quench on galaxy-wide scales, using Keck/ESI long-slit spectroscopy (Dickey et al. 2019). Despite their overall passive appearances, nearly all low-mass quiescent galaxies host AGN, in contrast to denser environments, where we observe significant numbers of quiescent galaxies lacking AGN signatures. These results suggest that the presence of hard ionizing radiation (AGN-like line ratios) is tied to the quenching of what may be the lowest-mass self-quenched galaxies. Complementary to these findings, this thesis also explores the quiescent fraction of low mass galaxies in isolation produced by large volume (L ≥ 100 Mpc) comsological and hydrodynamical simulations and how they compare to wide-field galaxy surveys. To make these comparisons meaningful, we create synthetic spectroscopic and photometric observations that replicate the characteristics of a particular galaxy survey, including noise and incompleteness. All the simulations included in the study fail to reproduce the observed absence of quiescent field galaxies below M* = 10^9 M⊙, suggesting that additional or alternate feedback mechanisms are required to quench low mass, isolated galaxies (Dickey et al. 2021). This thesis also explores the simulated low mass galaxy population in Local Group-like environments. By producing synthetic observations, we show that the simulations produce a population of faint, red satellites that have extremely old ages and represent either a population that has thus far been missed by observations or artifacts of unphysical processes in the simulations. This thesis demonstrates on the necessity of “apples to apples” comparisons as the basis of any meaningful measurement. By acknowledging and actively folding in observational biases to analyses of galaxy simulations, we highlight the significant discrepancy between current models of low mass galaxy quenching and observations of the galaxies themselves.

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