Comparing the Substructure of the Milky Way Galaxy to the Besançon Model

The Milky Way is a spiral galaxy, which has a rotating disc with spiral arms that spread outwards from a dense center and a stellar halo surrounding the disc. The formation of spiral galaxies is thought to follow the Hierarchal Merger Model where small dwarf galaxies accrete to form large objects. A galaxy's substructure, or its specific features, is greatly dependent on its accretion history. In this work, we examine the Milky Way's substructure to learn more about its accretion history. We used data from the Halo Assembly in Lambda-CDM: Observations in 7 Dimensions (HALO7D) survey, a survey of stars from 30 lines of sights with a combination of data from the Keck, Gaia, and Hubble telescopes. We compared this data to the Besançon model, a smooth multi-component model of the Milky Way with no substructure. We found that the Besançon model served as a good comparison to the HALO7D data for density of stars in relation to latitude as well as for proper motion versus color. However, due to the parallax error of Gaia telescopes, it differed from Besançon's prediction of proper motion versus distance. Future work can be done to compare the LOS velocities from Keck DEIMOS spectra of stars to further outline the substructure of the Milky Way.