The Panchromatic Hubble Andromeda Southern Treasury (PHAST) Survey: Resolved Stellar Photometry

The PHAST survey is creating a legacy map of the southern half of M31 with photometric data from Hubble Space Telescope observations with the Advanced Camera for Surveys (ACS) in the optical (F475W, F814W), and the Wide Field Camera 3 (WFC3) in the near ultraviolet (F275W, F336W). The near-infrared observations of this region can be added later with the Roman Space Telescope for a higher efficiency. The PHAST survey goes ~13 kpc along the southern major axis of M31 and should add roughly 100 million resolved stars to M31's stellar photometry archive. Our preliminary reductions of the first half of the observations suggest a similar depth in the UV to the completed Panchromatic Hubble Andromeda Treasury (PHAT) Survey, and a few tenths of a magnitude shallower in the optical because of shorter visit time. The PHAST survey will cover several structurally unique regions that belong to the southern disk of M31, including the intersections with M32 and the giant southern stream, the split portion of the star formation ring, and the southern bar. Moreover, these observations will allow us to further constrain the merger and accretion history of M31 as well as the formation and evolution of the M31 disk. We will provide an overview of the PHAST survey, including the current state of the data acquisition and reduction, as well as preliminary resolved stellar photometry and initial spectroscopic follow-up.