Developing Statistical Models for Analyzing Stellar Stream Characteristics

Stellar streams are unique galactic substructures that play a critical role in our understanding of galaxy formation and the galactic potential. They form as an intermediate stage as accreted globular clusters and dwarf galaxies are disrupted through tidal forces and merge with a host galaxy. This process is sensitive to the gravitational potential of the host galaxy and perturbations from other substructures within the galaxy. Because of this, Milky Way stellar streams are important tools for studying the formation history of the Milky Way and measuring its mass distribution. This thesis is divided into three chapters, first a discussion of the methods and statistical techniques used to study Milky Way stellar streams, and then two projects applying those methods to known stellar streams. For our first project, we take a broad look at a group of thirteen streams using photometry from three sky surveys: the Dark Energy Survey (DES), the Dark Energy Camera Legacy Survey (DECaLS), and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). We developed a flexible model that could be fit to all the streams with minimal modification between them. This allowed us to trace their tracks on the sky, create detailed stellar density maps, and derive additional characteristics like luminosity and stellar mass. With comparable measurements for a large number of streams, we then explored their group properties and how they compare to intact objects. Our second project was focused on a single stream, the Ophiuchus stellar stream. Recent spectroscopy from the Southern Stellar Stream Spectroscopic Survey (S5) and proper motion data from the Gaia survey were combined to fit the entire 6D stream track and identify new member stars. We used dynamical simulations in combination with the observed 6D track to look at the impact of the rotating bar on Ophiuchus and how it can be used to constrain bar parameters and the location of its progenitor. The improved radial velocity measurements and improved coverage of the stream by S5 also provided an opportunity to explore a spur-like feature above Ophiuchus. We confirmed this population was part of the stream and identified probable members and its position and velocity relative to the main track. Based on its position and stellar distribution, we concluded that the probable cause was likely the Milky Way’s rotating bar. We were able to reproduce similar bifurcations and spurs in dynamical simulations solely through bar interactions scattering stars.