BUILDING THE STELLAR HALO THROUGH FEEDBACK IN DWARF GALAXIES

We present a new model for the formation of stellar halos in dwarf galaxies. We demonstrate that the stars and star clusters that form naturally in the inner regions of dwarfs are expected to migrate from the gas-rich, star-forming center to join the stellar spheroid. For dwarf galaxies, this process could be the dominant source of halo stars. The effect is caused by stellar-feedback-driven bulk motions of dense gas which, by causing potential fluctuations in the inner regions of the halo, couple to all collisionless components. This effect has been demonstrated to generate cores in otherwise cuspy cold dark matter profiles and is particularly effective in dwarf galaxy halos. It can build a stellar spheroid with larger ages and lower metallicities at greater radii without requiring an outside-in formation model. Globular-cluster-type star clusters can be created in the galactic ISM and then migrate to the spheroid on 100 Myr timescales. Once outside the inner regions, they are less susceptible to tidal disruption and are thus long lived; clusters on wider orbits may be easily unbound from the dwarf to join the halo of a larger galaxy during a merger. A simulated dwarf galaxy (Mvir ≃ 109 M☉ at z = 5) is used to examine this gravitational coupling to dark matter and stars.