ASTRONOMY COLLOQUIUM

The Milky Way halo provides an unparalleled opportunity to map dark matter on small, subgalactic scales; a key regime for distinguishing competing models of dark matter. Stellar streams are particularly sensitive tracers of the halo gravitational potential. However, in addition to dark matter, baryonic objects like the Milky Way disk, bar, or its satellites, can also impact streams. Using the wealth of precise astrometric data from Gaia, we have recently been able to make progress on disentangling these by (1) discovering stream origins from their orbital histories, (2) simultaneously modeling tidal tails from multiple globular clusters to map the halo gravitational potential, and (3) uncovering evidence of stream perturbations in the outer, dark-matter dominated halo. However, due to their low mass, detecting truly dark, cold dark matter subhalos will require even more precise, ~100m/s, kinematics throughout the Galaxy. I will discuss the Via project, a full-sky Magellan and MMT survey aimed at delivering ~100 m/s radial velocities at G<20 in dozens of stellar streams (first light 2026), and ultimately discovering the nature of dark matter.