2) Chemical Abundances in the Stellar Disk and Inner Halo of Andromeda and the Milky Way

Abstract: The Milky Way (MW) is the template for our understanding of disk galaxy formation. However, there is growing evidence that the MW’s formation history sets it apart from its sister galaxy, Andromeda (M31), calling its status as a template into question. A direct way to probe galaxy formation history is through detailed chemical abundance measurements of individual stars. Until recently, such measurements were not available in M31, limiting the extent to which M31 could serve as a true complement to the MW. In this talk, I will present the first alpha-element abundance measurements of individual red giant branch stars in the inner halo and outer stellar disk of M31.With measurements for over 200 individual stars, the Elemental Abundances in M31 survey has produced the largest homogeneous set of chemical abundances in M31 to date. Based on this data, we have found that the outer disk of M31 is more alpha-enhanced than the outermost probed regions of the MW’s disk. Additionally, the inner stellar halo of M31 appears to be more alpha-enhanced and metal-rich than the inner stellar halo of the MW, although both galaxies may host accreted stellar populations with halo-like kinematics. I will discuss the implications of these results for M31’s formation history, focusing on a recent major merger scenario, and for its differences with respect to the MW.

Bio: Ivanna Escala is a Carnegie-Princeton Fellow at the Carnegie Observatories. She is an expert in measuring chemical abundances from low- and medium- resolution resolved stellar spectroscopy. She is interested in galactic archaeology and galaxy formation in the Local Group and Local Volume, with a focus on studies of M31.