| Abstract: |
Over the past several decades, observational and theoretical work has built a successful model for the relationship between galaxy formation and dark matter (DM). To test our understanding of this model, we can look for surprises from the extreme end of galaxy formation. Ultra-diffuse galaxies (UDGs), with central surface brightnesses greater than 24 magnitudes per square arcsecond and sizes greater than 1.5 kpc, present observational challenges to our standard model of galaxy formation. In this talk, I present dynamical modeling of the stars and star clusters of two UDGs which place them on opposite ends of the mass spectrum. The first one, NGC 1052-DF2, shows a deficit of dark matter, with the available kinematic data being consistent with no DM at all. In constrast the Coma Cluster UDG DF44 shows evidence of its dynamics being dominated by DM. With its relatively high DM halo mass, DF44 presents a new observational test for Fuzzy Dark Matter, in which DM consists of an ultra-light boson manifesting wave-like behavior on astrophysical scales. Throughout the talk, I discuss the difficulties, both observational and statistical, in making robust inferences for these extreme cases.
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