Satellites and stellar streams of the Andromeda Galaxy

Abstract

One of the theories of galactic evolution is that large structures grow, hierarchically, from the merger and accretion of smaller ones. Evidence for this lies in the spectacular stellar streams observed around the Milky Way, Andromeda and other galaxies within and beyond the Local Group. In this thesis I study two stellar structures in the outer halo of Andromeda: the North West Stream (NW Stream) and an intriguing filamentary feature, the Eastern Extent located proximate the Giant Stellar Stream. The NW Stream comprises two separate segments thought to be parts of a single structure entwined around Andromeda. The upper segment of the NW Stream is co-located on-sky with the dwarf Spheroidal galaxy Andromeda XXVII. Using data from the Pan-Andromeda Astronomical Survey, I compare the kinematic and spectroscopic properties of these two features and find it plausible that Andromeda XXVII is being tidally disrupted by Andromeda and could be the progenitor of the upper segment of the NW Stream. Comparing velocity gradients and model orbits for both segments of the NW Stream, I find evidence that they are both infalling towards Andromeda indicating that it is unlikely that the NW Stream is a single structure. I also derive predictions for the proper motions for both stream seg- ments, which I find to be consistent with similar predictions for Andromeda and Andromeda XXVII. With respect to the Eastern Extent, I find it has kinematic and photometric properties consistent with other nearby features, i.e. Stream B and one of the substructures in Stream C, Stream Cr, plausibly linking these features. When I compare my results for the Eastern Extent to the properties of the Giant Stellar Stream I find that the Eastern Extent could plausibly comprise stars stripped from the progenitor of the Giant Stellar Stream. I conclude that further modelling is required to determine how the Giant Stellar Stream, the Eastern Extent and Streams B and Cr were formed.