Location: TAAC 66
Scientific Advisor: Michael D. Gladders
Affiliations: Kavli Institute for Cosmological Physics
Ph.D. Thesis Defense (Astronomy)
Defense date: July 13, 2015
Ph.D. Committee members: Hsiao-Wen Chen, Andrey Kravtsov, Rich Kron
"Dr. Louis Abramson is an expert on the observation and phenomenological modeling of galaxy evolution, with a particular focus on the relationship between bulk statistical observables of galaxies, such as the distributions of star-formation-rate and mass over cosmic time, and the star formation histories of galaxies. His work during his Ph.D. has led to several new insights into the relationship between the passive (i.e., bulges) and actively star-forming components of galaxies, and led to a clear understanding that the scatter of galaxies across the so-called 'star forming main-sequence' is a critical observable to consider in further analyses, which he will continue as a postdoc at UCLA."
- Michael D. Gladders, Ph.D. advisor
Thesis Abstract: Galaxy star formation histories (SFHs) form a central thread of the cosmological narrative. Understanding them is therefore a central mission of the study of galaxy evolution. Although an ever-better picture is emerging of the build-up of the stellar mass of the *average* galaxy over time, the relevance of this track to the growth of *individual* galaxies is unclear. Largely, this ambiguity is due to the availability of only loose, ensemble-level constraints at any redshift appreciably greater than zero. In this talk, I outline how one of these constraints -- the the star formation rate/stellar mass relation -- shapes empirically based SFH models, especially in terms of the *diversity* of paths leading to a given end-state. I show that two models propose very different answers to this question -- galaxies grow *together* vs. galaxies grow *apart* -- corresponding (largely) to two different interpretations of the scatter in instantaneous galaxy growth rates at fixed stellar mass -- unimportant vs. essential. I describe how these interpretations affect one's stance on the profundity of galaxy "bimodality," the role of quenching mechanisms, and the influence of environment on galaxy evolution. Finally, after endorsing one of the models, I present some predictions that --- given upcoming observations --- should have the power to prove me right or wrong.
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