Special Physics Colloquium

Insights into dark matter from the stellar halos of galaxies

Cosmological simulations can now make specific and detailed predictions for theshapes, masses, and substructure fractions in galactic dark matter halosthat depend on the dark matter model assumed. Comparing these predictions tothe observed mass distributions of galaxies should in principle lead toconstraints on the nature of dark matter, but observable dynamical tracers canbe scarce in regions where the dark matter distribution is best able todiscriminate between models. One such region is the distant outskirts ofgalaxies, where the influence of baryonic matter on the dark matter halo islimited and the effect of dark substructures most prominent. New surveysof Milky Way stars like Gaia, alongside next-generation instrumentsand giant telescopes, are for the first time providing accurate positions,velocities, and abundances for large numbers of stars in faint tidal streams:remnants of tidally-disrupted satellite galaxies that trace out the massdistribution in the distant reaches of galaxy halos. I will show how state-of-the-artsimulations play a crucial role in interpreting and analyzing this wealthof new information about stellar halos, and how stellar haloobservations over the next decade will characterize the dark matterdistribution in galaxies, test theories of the nature of dark matter, andilluminate the role of dark matter in galaxy formation.