Karoline Gilbert (U Washington)

Stellar Halo Formation in a Hierarchical Universe: Lessons from Our Sister Galaxy Andromeda

In the paradigm of hierarchical galaxy formation, massive galaxies are built through a series of major and minor merger events. A consequence of hierarchical galaxy formation is that galactic stellar halos should be at least partially composed of tidal debris from past accretion events. In order to increase the observational constraints on theories of stellar halo formation, we have undertaken a large Keck/DEIMOS spectroscopic survey of individual red giants in Andromeda's stellar halo. I will review what we have learned from stellar kinematics about M31's extended stellar halo and merger history, and compare our observations of the structure and substructure of M31's stellar halo with predictions from simulations of stellar halo formation via accretion.