Presentation #123.08 in the session Evolution of Galaxies II.
Modern spectroscopic studies of resolved stellar populations in the Andromeda (M31) system will serve to connect the Local Group to the Local Volume for future observations. As a consequence, our understanding of M31’s merger history will serve as the foundation upon which we interpret the next observational frontier. Outstanding questions remain concerning M31’s assembly history: has its disk survived a major merger within the last few Gyr, and does this major merger coincide with the formation of M31’s Giant Stellar Stream (GSS) and its various tidal shells? In this talk, I will present novel results from the Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo (SPLASH) survey on M31’s Northeast shelf. For the first time, I will show that this structure agrees with expectations of a tidal shell formed in a radial merger and provides strong evidence in favor of predictions of GSS formation models in which the shelf originates from the second orbital wrap of the tidal debris. In combination with M31’s West and Southeast shelves, this data represents the first complete kinematical detection of a galactic shell system in the local universe. I will conclude by discussing the implications of shelf chemodynamics for M31’s broader merger history.