Simulations of Local Group Galactic Interactions

Abstract

As the nearest galactic laboratory available for study, the Local Group harbors the faintest and most dark-matter dominated known galaxies. The sample of observed dwarf satellites surrounding the Milky Way and Andromeda is continually growing, and so is the list of diverse detected substructures in the outer reaches of our Galaxy's halo. Knowledge of our own cosmic backyard is especially critical to building up our understanding of the Universe at large. In this effort, simulations are our only access to the time axis, as they allow us to reconstruct past possible histories of the interplay between members of the Local Group. In this thesis, I have developed a hybrid test particle/$N$-body approach to modeling interactions between galaxy pairs. The method overcomes computational challenges by leveraging semianalytic speed for parameter exploration, while relying on $N$-body simulations for followup morphological analysis. This approach is used to model the past collision between Andromeda and M32, highlighting an inclined high impact parameter collision as a possible architect for the ring-like structure of Andromeda's disk (Chapter 2). Inspired by recent insights about the mass of the Sagittarius dwarf galaxy, I have built a new model for the past orbit of Sagittarius and the resulting stellar stream (Chapter 3). The model is in good agreement with the most distant stream structure known in the Milky Way, and furthermore predicts tidal debris reaching all the way to the edge of the halo. Using this model of the Sagittarius orbit, I place constraints on the virial mass of the Milky Way (Chapter 4). Finally, my model data is compared with a new sample of RR Lyrae stars and used to identify a new spur of the Sagittarius stream extending 30~kpc beyond the previously detected apocenter (Chapter 5). Together these results provide a framework for reconstructing past events in the Local Group archaeological record.