Abstract:
Over the last decade, the number of dwarf galaxies known around the Milky Way and M31 has more than doubled. This recently discovered population includes dwarf galaxies with less than one millionth of the Milky Way’s own luminosity. The number, spatial distribution, and densities of nearby, ultra-faint dwarfs are being used to test dark matter+galaxy formation models, and their locations are being targeted by dark matter detection experiments aiming to constrain the particle nature of dark matter. To fully exploit these dwarfs as probes of dark matter on galaxy scales requires a well-defined census that is as complete and unbiased as possible. I will give an overview of our current observational understanding of the demographics of Milky Way and M31 dwarf galaxies, and the ways that observational bias still limits our view and interpretation of these populations. I will discuss what imminent and future wide-field surveys, such as DES and LSST, may reveal about ultra-faint dwarf galaxies and their relationship with dark matter halos. I will also highlight some interesting technical challenges (and possible solutions) facing searches for ultra-faint dwarfs in the next generation of surveys.