The Milky Way halo in the Gaia era

Ana Bonaca (Harvard CfA) - March 20, 2017 at 12:10 pm

Stellar halos are composed of stars formed in situ, as well as stars accreted from satellites. The accretion remnants provide spectacular evidence that galaxies form, at least in part, hierarchically, while the in situ component provides a window into the host galaxy in its infancy. However, due to the short dynamical times, both components appear well mixed in the inner halo, and are observationally challenging to disentangle. Combining the first year of Gaia data with ground-based spectroscopic surveys, we identified a metal-rich component of the stellar halo of the Milky Way. Based on their orbital properties, we argue that these stars were formed in situ. A comparison to a high-resolution hydrodynamical simulation Latte further suggests that these in situ stars predominantly originate from the inner Galaxy and have subsequently migrated to the Solar circle. In the outer halo, the dynamical times are longer, so the accretion events remain coherent and are identified as tidal streams. These streams are shaped by the underlying gravitational potential, and we show how to optimally map the distribution of matter in the Galaxy by forward-modeling tidal streams. The upcoming Gaia measurements will further improve these constraints, thus revolutionizing our understanding of both the stellar and the dark matter halo of the Milky Way.

The seminar will be held in 131A Campbell Hall.

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