Abstract:
Galaxies are not static islands of stars; they are dynamic systems shaped by billions of years of cosmic collisions. When a large satellite galaxy merges with a host like our Milky Way, it leaves behind a diffuse, extended cloud of debris known as a stellar halo. Because these stars are stripped from the incoming satellite, the amount of stars, their ages and compositions, and motions provide crucial information about a galaxy's past merger events. I will highlight work done in our group on measuring stellar halos by resolving them into individual stars, and efforts to infer merger histories from stellar halo properties. These halos reveal that galaxies appearing similar to the Milky Way can have incredibly different merger histories, with measurable effects on the galaxies' history of star formation and structure.