The Panchromatic Hubble Andromeda Treasury
J. J. Dalcanton, B. F. Williams, D. Lang, T. R. Lauer, J. S. Kalirai,, A. C. Seth, A. Dolphin, P. Rosenfield, D. R. Weisz, E. F. Bell, L. C., Bianchi, M. L. Boyer, N. Caldwell, H. Dong, C. E. Dorman, K. M. Gilbert, L., Girardi, S. M. Gogarten, K. D. Gordon, P. Guhathakurta

TL;DR
The PHAT survey uses Hubble Space Telescope imaging across multiple wavelengths to resolve over 100 million stars in M31, providing detailed data on stellar populations, structure, and star formation history.
Contribution
This work presents a comprehensive, multi-wavelength imaging survey of M31's star-forming disk, including data acquisition, photometry, and initial structural analysis, which advances understanding of galaxy structure and stellar populations.
Findings
Resolved over 100 million stars in M31.
Identified the 10 kpc ring as a stellar overdensity with older stars.
Provided detailed photometric data across UV to NIR wavelengths.
Abstract
The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going HST Multicycle Treasury program to image ~1/3 of M31's star forming disk in 6 filters, from the UV to the NIR. The full survey will resolve the galaxy into more than 100 million stars with projected radii from 0-20 kpc over a contiguous 0.5 square degree area in 828 orbits, producing imaging in the F275W and F336W filters with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with WFC3/IR. The resulting wavelength coverage gives excellent constraints on stellar temperature, bolometric luminosity, and extinction for most spectral types. The photometry reaches SNR=4 at F275W=25.1, F336W=24.9, F475W=27.9, F814W=27.1, F110W=25.5, and F160W=24.6 for single pointings in the uncrowded outer disk; however, the optical and NIR data are crowding limited, and the deepest reliable magnitudes are up to 5 magnitudes brighter…
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