Assigned ID: 689 ----- Attempting Submission 1 (Fri Feb 24 20:49:10 GMT 2012) ----- Over the past decade, HST has obtained deep color-magnitude diagrams (CMDs) of a large number of nearby galaxies. These data have allowed the age-metallicity degeneracy to be broken and the age-metallicity relation (AMR) of stars within these galaxies to be empirically derived. However, the theoretical predictions of the AMR in a LambdaCDM universe have lagged behind: interpretation of the observations usually rests on simple untested expectations. Our pilot study of the AMR within a simulated galaxy generated in a full cosmological context has revealed a wealth of structure that is not anticipated by the simple models, including abundant substructure, a broad age-metallicity distribution, and non-monotonic evolution. It is now clear that interpretation of the HST observations requires a thorough theoretical analysis of the AMR in a large sample of galaxy formation simulations; this will be particularly critical for the large ACS Nearby Galaxy Survey Treasury (ANGST) and Panchromatic Hubble Andromeda Treasury (PHAT) programs that together invest over 1000 orbits to obtain spatially-resolved AMRs. We propose to perform such a study, using the 16 SPH simulations of galaxies from the McMaster Unbiased Galaxy Simulations (MUGS) and 19 adaptive mesh galaxy simulations from the Ramses Disk Environment Study (RaDES). This analysis will enable us to predict how the chemical enrichment histories of different galactic components and galaxies with different accretion and merger histories differ, how substructures in age-metallicity space relate to dynamical events in the history of the galaxy, and how well the AMR can be reconstructed from observed HST CMDs. RESOLVED STELLAR POPULATIONS 12 Medium false 0.0 0.0 false false true false SUPPORTED