Program: GN-2020A-FT-104

The satellite systems of the Milky Way and Andromeda have proved extremely fruitful testing grounds for our concordance cosmology model. However, to fully understand small-scale structure, it is crucial to characterize a statistical sample of satellite systems around other MW-like galaxies. We have developed and tested machinery to use surface brightness fluctuations to obtain distances to low mass satellites, allowing us to characterize satellite systems much more efficiently than previously possible and roughly double the number of known systems using archival data alone. We see hints that all of our satellite systems are more centrally concentrated than expected from simulations of MW-mass hosts. However, to robustly characterize the radial distribution of satellites, it is important to survey satellite systems out to the virial radius of the host. We have used shallow ground based imaging to identify 7 additional candidate satellites of the most concentrated host in our sample, NGC 4631, out to a projected separation of 260 kpc. We propose to use Gemini/GMOS to acquire deeper images of these candidates to measure SBF distances and classify each dwarf as either a satellite of NGC 4631 or a background contaminant. This will let us fully test if the strong central concentration occurs at all radii or just its innermost region.