Collaborative Research: Stellar Clouds as New Probes of the Milky Way's Accretion History and Mass Distribution.

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What are the radial profiles, shapes, extents and orientations of the dark matter halos that surround galaxies? This fundamental question is particularly difficult to address in the outskirts of galaxies where there are few visible tracers. Perhaps the most promising approach is to use stellar debris from the destruction of satellite galaxies, and the most promising place to try this approach is the Milky Way - the one galaxy in the Universe where a halo's 3-dimensional structure (rather than a 2-dimensional projection) can be directly probed.This award will support a combined observational and theoretical approach to providing a new and powerful perspective on accreted halo substructures, and, in particular, poorly-studied stellar clouds. The observational program focuses on obtaining radial velocities for stars in known stellar clouds, and making connections between debris structures - from the Solar vicinity to the outer Galaxy, and from one side of the Galaxy to another. Such connections will yield the first comprehensive maps of these stellar debris structures on Galactic scales. Interpreting these maps with a systematic suite of simulations will fill in our missing knowledge of the Galaxy's accretion history and matter distribution.This award will support the training of one minority student in their transition from undergraduate to graduate school through participation in Columbia's "Bridge to the PhD" program. It will also enable the PIs to actively engage students, amateur astronomers and the general public in building an understanding of the history of our home galaxy.