Coral Wheeler (Cal Poly Pomona): "How invisible stellar halos bias our understanding of ultra-faint galaxies"

Accurately measuring the properties of ultra-faint galaxies (UFDs) is critical for testing dark matter and galaxy formation models. Recent observations suggest that UFDs may contain stars extending well beyond multiple half-light radii, raising the possibility that we are missing a small but significant fraction of their stellar populations at low effective surface brightness near the outskirts. Using 19 ultra high-resolution FIRE-2 galaxies, I will demonstrate how inferred UFD properties change when measurements are limited by realistic effective surface-brightness cuts. We find that applying these cuts brings simulated UFD sizes into better agreement with observations, while also affecting inferred stellar masses, average metallicities, and even dark matter masses. These biases can result in incorrect total mass measurements, which may impact the ability to use these systems to effectively test dark matter models.