Measuring Star Formation Histories, Distances, and Metallicities with Pixel Color–Magnitude Diagrams. II. Applications to Nearby Elliptical Galaxies

摘要

We present spatially resolved measurements of star formation histories (SFHs), metallicities, and distances in three nearby elliptical galaxies and the bulge of M31 derived using the pixel color–magnitude diagram (pCMD) technique. We compute pCMDs from archival Hubble Space Telescope photometry of M87, M49, NGC 3377, and M31, and we fit the data using the new code PCMDPy. We measure distances to each system that are accurate to ～10%. The recovered nonparametric SFHs place reasonable (±1 dex) constraints on the recent (<2 Gyr) star formation in M31 and NGC 3377, both of which show evidence of inside-out growth. The SFHs in M87 and M49 are constrained only at the oldest ages. The pCMD technique is a promising new avenue for studying the evolutionary history of the nearby universe and is highly complementary to existing stellar population modeling techniques.