Elemental Abundances in the Local Group: Tracing the Formation History of the Great Andromeda Galaxy

Citation

Escala, Ivanna Ashley (2020) Elemental Abundances in the Local Group: Tracing the Formation History of the Great Andromeda Galaxy. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/16bk-vm98. https://resolver.caltech.edu/CaltechTHESIS:05292020-133139370

Abstract

The Local Group (LG) is an environment accessible to detailed studies of galaxy formation, providing a complement to the early universe. In particular, spectroscopy of resolved stellar populations in the LG provides kinematical and chemical information for individual stars that can be used to infer the history of L_★ galaxies like the Milky Way (MW) and Andromeda (M31).

The Gaia revolution in the MW, combined with spectroscopy from APOGEE and other surveys, has enabled comprehensive observational studies of the MW's formation history. In addition, comparisons to simulations can be leveraged to maximally utilize such observational data to probe the hierarchical assembly of galaxies. Toward this goal, I have analyzed simulations of chemical evolution in LG dwarf galaxies to assess their ability to match observations.

The exquisite detail in which the MW has been studied is currently not achievable in any other L_★ galaxy. For this reason, the MW is a template for our understanding of galaxy formation. M31 is the only external galaxy that we can currently hope study in a level of detail approaching the MW. Studies of M31 have recently taken on greater significance, given the growing body of evidence that its formation history differs substantially from that of the MW.

In an era of limited information about elemental abundances in M31, I have developed a technique to apply spectral synthesis to low-resolution stellar spectroscopy in order to measure abundances for individual giant stars in distant LG galaxies. Through undertaking the largest deep, spectroscopic survey of M31 to date with my collaborators, this has resulted in the first measurements of the elemental abundances in the inner stellar halo and stellar disk of M31, and the largest homogeneous catalog of elemental abundances in M31. With this foundational work, we have opened the doors to detailed studies of the chemical composition of M31.

Now, we can begin to ask--and answer--what differences in the elemental abundances of the M31 and the MW imply for our knowledge of galaxy formation in the broader universe. At the cusp of next-generation observational facilities and theoretical simulations, we can only advance toward this goal.

Thesis Files