Three WFIRST Science Cases for Local Volume Galaxies: Milky Way Halo Star Proper Motions, the Edge of M31's Stellar Halo, and Globular Clusters in the Virgo Cluster
I will discuss three sample WFIRST near-field cosmology science cases that all involve studies of the dark matter content, accretion history, and chemical enrichment history of Local Volume galaxies. The first of these science cases involves measuring the proper motions of faint stars in the remote halo of the Milky Way by using multi-epoch WFIRST images or by combining astrometry from single-epoch WFIRST images with earlier epoch astrometry from Gaia and HST. This could extend the domain of precise astrometry by 2 mag compared to what Gaia alone is capable of. The second science case involves mapping the stellar halo of M31 out to r ~ 300 kpc and characterizing the "edge" of the halo at the splashback radius. The third science case involves the identification and study of globular clusters in the nearby Virgo cluster of galaxies. Most of these globular clusters are satellites of Virgo cluster galaxies but some are intracluster globular clusters that have been stripped from their original host galaxies.