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SkyMapper Protected Science Project

Exploring the Halo of the Galaxy with SkyMapper

Gary Da Costa (RSAA), Andy Casey (Cambridge), Ken Freeman (RSAA), Stefan Keller (RSAA), Dougal Mackey (RSAA), Chris Owen (RSAA)

In the current cosmological paradigm large galaxies like the Milky Way are built-up through the merger and accretion of lower mass systems, predominantly at early epochs. In the inner parts of the Galaxy the spatial and kinematic signatures of this process have been erased by the relatively short dynamical timescales but in the outer parts of the Galactic halo, where dynamical timescales are long, there is considerable evidence that supports the hierarchical assembly picture. The outstanding unresolved question, however, is what fraction of the stars in the halo today originated in the tidal disruption of satellite galaxies. The SDSS results indicate that this fraction is probably quite high but additional constraints from the southern hemisphere sky are needed. The SkyMapper filter system is designed for optimal use in stellar programs, providing information on stellar gravities and metal abundances. Coupled with multi-epoch imaging, SkyMapper photometry will allow us to isolate particular types of halo tracers, which can then be used to investigate the stellar distribution, and the degree of sub-structure, in the Galactic halo. The halo tracers include RRL variables and blue horizontal branch stars, which can function as standard candles, and metal-poor red giants which potentially sample distances to ~100 kpc. The program will use Main Survey data.