"The Age of Andromeda"
As the nearest
spiral galaxy to our own, Andromeda offers an ideal laboratory for the
study of galaxy formation. We are investigating the star
formation history in Andromeda's halo, outer disk, and giant tidal
stream via a series of extremely deep observations using the Advanced
Camera for Surveys on the Hubble Space Telescope. These are the
first observations to directly characterize the age distribution in
Andromeda, using the of colors and luminosities of the main sequence
stars. Unlike the ancient, metal-poor halo of the Milky Way, the
Andromeda halo is populated by stars with a surprisingly wide range of
age and metallicity. These findings suggest a more violent merger
history in Andromeda than that in the Milky Way. I review these
results and others enabled by these rich datasets.