Event Details

Dr. Richard Anthony D'Souza, Postdoctoral Researcher, University of Michigan, presents this seminar sponsored by the Physics & Astronomy Department.

Although galaxy merging and interactions are the key, distinctive features of our picture of galaxy formation in a hierarchical Universe, they have nonetheless played a peripheral role in our observational understanding of disk-dominated Milky Way-mass galaxies. The Andromeda Galaxy (M31), our nearest large galactic neighbour, offers a unique opportunity to test how mergers affect galaxy properties. M31's stellar halo caused by the tidal disruption of satellite galaxies is the best tracer of the galaxy's accretion history. Despite a decade of effort in mapping out M31's large stellar halo, we are unable to convert M31's stellar halo into a merger history. Here we use cosmological models of galaxy formation to show that M31’s massive and metal-rich stellar halo containing intermediate age stars implies that it merged with a large (M* ~ 2.5 x 10^10 M_sun) galaxy ~2 Gyr ago.