The Star Formation Histories of the Bulge and Disk of M31 from Resolved Stars in the Near-Infrared

We discuss H and K observations of three fields in the bulge and disk of M31obtained with the Altair adaptive optics system and NIRI instrument on GeminiNorth. These are the highest resolution and deepest near-infrared observationsobtained to date of the inner regions of M31, and demonstrate the promise ofground-based adaptive optics for studying the crowded regions of nearbygalaxies. We have combined our observations with previously publishedHST/NICMOS observations of nine M31 fields and have derived the coarse starformation histories of M31's bulge and inner disk. From fits to the M_Kluminosity functions, we find the stellar population mix to be dominated byold, nearly solar-metallicity stars. The old populations, which we define ashaving age >~6 Gyr, indeed dominate the star formation histories at all radiiindependent of the relative contributions of bulge and disk stars. Although allof our fields contain some bulge contribution, our results suggest that thereis no age difference between the bulge and disk to the limit of our precision.Comment: 65 total pages, 22 figures, accepted for publication in the Astronomical Journa