Revealing the Merger Histories of Nearby Galaxies from their Stellar Halos with Roman

Galaxies like the Milky Way (MW) host vast halos of stars accreted from past merger and accretion events. While the brightest structures can be studied using traditional imaging, the resolved stellar populations are the most information-rich tracers of this accreted material. The incredible wide-field of Roman, combined with the depth of JWST, will drive a new era of stellar halo science in the Local Volume. This effort will be made possible by important synergy with ground-based studies of the resolved stellar halo populations around nearby galaxies, including the upcoming Rubin LSST. From this ongoing foundational ground-based work, we have learned that the stellar halos of galaxies similar in mass to the MW are incredibly diverse. Yet, challenges unique to ground-based studies, such as poor star-galaxy separation, make more complex inferences, such as the ages, abundances, and substructure of these halos, very difficult. This is particularly relevant in galaxies' inner halos, where the disk and accreted populations are nearly indistinguishable. I will show that by utilizing the combined FOV of Roman and sensitivity of JWST, we can revolutionize our understanding of the merger histories of nearby galaxies, and decode the properties of their complex stellar halos more precisely than ever before.