Understanding the Stellar Mass Growth and Quenching of Massive Galaxies

Abstract

One of the first remarkable studies in the field of galaxy evolution determined that there are two distinct types of galaxies based on their morphologies: spirals and ellipticals. We’ve since found that spirals tend to be blue, lower-mass, gas-rich, star-forming galaxies. On the other hand, ellipticals tend to be red, massive, gas-poor, quiescent galaxies. This “galaxybimodality” is still being studied today, as we have many unanswered questions about the origin of its existence. For example, how do star-forming galaxies grow in stellar mass? And what physical processes are responsible for the cessation of star formation in quiescent galaxies? In this dissertation, I explore the stellar mass growth and quenching of massive galaxies. I use a sample of high redshift (6.7 < z < 13.2) galaxies to study how varying the initial mass function (IMF) changes their inferred stellar masses, showing that a redshift-dependent IMF infers reduced stellar masses in the high redshift universe. Next I explore the heterogeneity ofmolecular gas reservoirs in quiescent galaxies, showing that quiescent galaxies with detectable gas reservoirs have evidence of secondary bursts of star formation, likely driven by gas-rich minor mergers. Furthermore, I explore the connection between active galactic nuclei (AGN) activity and suppressed star formation, and show that even with high quality data and gold-standard star formation history (SFH) modeling, it is difficult to find observational evidence of AGN-driven quenching. Finally, I investigate the star formation and chemical enrichment histories of massive, quiescent galaxies as a function of their structural and environmental properties, finding that galaxies are quenched through a complex interplay of physical mechanisms.