Using Star Clusters as Tracers of Star Formation and Chemical Evolution: the Chemical Enrichment History of the Large Magellanic Cloud

The star formation (SFH) and chemical enrichment (CEH) histories of Local Group galaxies are traditionally studied by analyzing their resolved stellar populations in a form of color-magnitude diagrams obtained with the Hubble Space Telescope. Star clusters can be studied in integrated light using ground-based telescopes to much larger distances. They represent snapshots of chemical evolution of their host galaxy at different ages. Here we present a simple theoretical framework for the chemical evolution based on the instantaneous recycling approximation (IRA) model. We infer a CEH from a SFH and vice versa using observational data. We also present a more advanced model for the evolution of individual chemical elements which takes into account the contribution of supernovae type Ia. We demonstrate that ages, iron and $\alpha$-element abundances of 15 star clusters derived from fitting of their integrated optical spectra reliably trace the CEH of the Large Magellanic Cloud obtained from resolved stellar populations in the age range 40Myr$<t<$3.5Gyr. The CEH predicted by our model from the global SFH of the LMC agrees remarkably well with the observed cluster age-metallicity relation. Moreover, the present day total gas mass of the LMC estimated by the IRA model ($6.2\cdot10^8 M_{\odot}$) matches within uncertainties the observed HI mass corrected for the presence of molecular gas ($5.8\pm0.5\cdot10^8 M_{\odot}$). We briefly discuss how our approach can be used to study SFHs of galaxies as distant as 10Mpc at the level of detail that is currently available only in a handful of nearby Milky Way satellites.
Comment: ApJ in press, 10 pages, 5 figures