Searching for stellar streams in the outer Milky Way halo

The main goal of this project is to help conduct the first systematic high-contrast search for stellar streams in the remote outskirts of the Milky Way. Large galaxies like our own are surrounded by diffuse envelopes of stars that extend to very large radial distances. These stellar halos are a natural consequence of hierarchical formation processes, where the growth of large galaxies is powered by the continual accretion and destruction of smaller systems. Locating and measuring the stellar streams from such events in principle allows the accretion history of a galaxy to be reconstructed. Moreover, the orbits of such streams can be used to accurately infer the properties of the underlying gravitational field, which is dominated by the influence of the host galaxy’s dark matter halo.

Due to our location inside the Milky Way, blind mapping of its stellar halo requires very deep imaging across the entire sky. As a consequence, very little is known about the outer regions of our Galaxy beyond radii of ~50 kpc. However, we know from studies of nearby galaxies such as Andromeda that remote globular clusters are excellent pointers to stellar streams. In this project you will use deep wide-field imaging from the state-of-the-art Dark Energy Camera to search the ultra-faint peripheries of distant globular clusters and discover new stellar streams in the outer Milky Way. These have the potential to serve as powerful probes of the Galactic dark matter halo at previously inaccessible radii.

Early results from this project have been extremely encouraging, with the discovery that some globular clusters are embedded in extended diffuse envelopes, plus the discovery of two of the most remote known tidal streams in the Milky Way halo.