Collaborative Research: Dark Matter and Substructure in the Galactic Halo with Gaia and Multi-Object Spectroscopy

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The Galactic Halo encompasses the vast, seemingly empty volume surrounding our home galaxy, the Milky Way. But the Halo is not so empty as it appears. A rich variety of dwarf galaxies, stellar streams and star clusters pervade the Halo. These structures can reveal the nature of dark matter, how heavy elements are made, and how our Galaxy formed. This project advances the field by combining data from large public sky surveys with new data to be obtained with state-of-the art ground-based facilities. This project aims to identify new stellar structures, then probe their chemistry and dynamics. The results will test competing models of dark matter and galaxy formation. This project builds on previous NSF investments in instrumentation and the scientific workforce. The team will continue to operate the NSF-funded Michigan/Magellan Fiber System (M2FS) spectrograph, enabling innovative science by other astronomers. These activities promote science by continuing successful public outreach programs and training the next generation of astronomers.The primary scientific objectives include 1) the detection of faint and previously unknown star clusters, dwarf galaxies, and stellar streams within the Milky Way halo; 2) measurement of the velocities and chemical compositions of the stars within these structures; and 3) mapping the dark matter content of these structures. To discover new objects, the team will mine data from the Gaia space mission, exploiting its unprecedented combination of sky coverage, precision of stellar positions, and measurement of stellar motions. The team will use Gaia data to identify not only new stellar structures, but also rare stars within known structures. For all such targets, the team will use the M2FS spectrograph to measure stellar velocities and chemical composition. Finally, the team will combine the Gaia and M2FS data sets, exploiting the multi-dimensional information to infer the dark matter content and chemical evolution of these structures. These results will advance the frontiers of knowledge regarding the nature of dark matter, the origin of heavy elements, the formation and evolution of the smallest galaxies, and the processes that built up the stellar halo of our own Milky Way.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.