The Panchromatic Hubble Andromeda Southern Treasury (PHAST)

The Panchromatic Hubble Andromeda Southern Treasury (PHAST) is a large 195-orbit Hubble Space Telescope program designed to map roughly 0.45 square degrees of the southern half of M31’s star-forming disk at optical and near-ultraviolet (NUV) wavelengths. The PHAST survey extends the northern coverage of the Panchromatic Hubble Andromeda Treasury (PHAT) down to the southern half of M31, covering out to R~13 kpc along the southern major axis and, in total, roughly 2/3 of M31’s star-forming disk. The PHAST survey covers key diagnostic features that are sensitive to M31’s complex merger history, which were previously unconstrained by the northern disk observations alone. PHAST creates a legacy map with stellar photometry of over 90 million resolved stars using HST’s resolution and sensitivity, enabling a wide range of scientific endeavors.