THE STELLAR CONTENT OF THE POST-STARBURST S0 GALAXY NGC 5102

Abstract

The stellar content of the S0 galaxy NGC 5102 is investigated using deep r' and i' images obtained with GMOS-S. A modest population of bright main-sequence stars and red supergiants is detected throughout the western portion of the disk. Based on the numbers of main-sequence stars, the star-formation rate (SFR) in NGC 5102 during the past ten million years is estimated to have been 0.02 M ? year. The majority of red giant branch (RGB) stars in the disk of NGC 5102 have [M/H] between ?0.9 and ?0.1, and the metallicity distribution of RGB stars at intermediate galactocentric radii peaks near [M/H] ~?0.6. RGB stars are traced out to galactocentric distances of 10 kpc, which corresponds to ~14 disk scale lengths. A large population of bright asymptotic giant branch stars is seen throughout the western portion of the disk, and the youngest of these have log(t yr) ~ 8.1. It is concluded that (1) stars that formed within the past Gyr comprise ~20% of the total stellar disk mass and (2) the SFR during intermediate epochs in the disk of NGC 5102 was at least 1.4 M ? year. Thus, large-scale star formation occurred throughout the disk of NGC 5102 at approximately the same time that similar elevated levels of star formation occurred in the bulge. It is suggested that NGC 5102 was a spiral galaxy that experienced a galaxy-wide episode of star formation that terminated a few hundred Myr in the past, and that much of its interstellar medium was ejected in an outflow.