Research Division Seminar
Ultra-Diffuse Galaxies (UDGs) and the Stellar Mass – Halo Mass Relationship

Abstract

The stellar mass – halo mass relationship is a fundamental scaling relationship connecting galaxies from dwarfs to giants to their dark matter halos. This relationship is currently key to our understanding of the complex interplay between the many modes of feedback (e.g., stellar winds, supernovae, AGN) and star formation in galaxies. However, recently a population of large half-light radius, low surface brightness ultra-diffuse galaxies (UDGs) have questioned our understanding of galaxy formation in the dwarf galaxy regime. UDGs have been found to reside in dark matter halos of widely varying mass. While many likely reside in "normal" dark matter halos for their stellar mass, some may exhibit an extreme lack of dark matter while yet others are extremely dark matter rich. In this talk, I give an overview of the current observational evidence for UDGs residing in massive dark matter halos. I place particular emphasis on my own Keck observations which have provided support for UDGs' unexpected stellar mass – halo mass positioning and that has revealed the internal structure of their halo (i.e., core vs cusp nature). I discuss how these observations currently inform proposed formation scenarios for UDGs and show an outstanding tension of my observations with simulations of galaxy formation. I conclude with a brief discussion of the important future goals of the field.