Metallicity indicators across the spectrum of composite stellar populations

With a chemically consistent evolutionary synthesis approach we follow the enrichment of individual chemical elements in the ISM. We describe the time With a chemically consistent evolutionary synthesis approach we follow the enrichment of individual chemical elements in the ISM. We describe the time evolution of broad band colors U to K and metal indices (Fe5335, Fe5270, Mg2, Mgb), taking into account the increasing initial metallicities of successive generations of stars. Using specific star formation prescriptions for the different spectral types of galaxies, we show our model galaxy broad band colors, synthetic spectra, and ISM abundances are in agreement with observations of nearby samples and template galaxies of the respective spectral types. We compare our synthetic Mg2 indices with observations and study the time evolution of the stellar index [MgFe] for composite elliptical galaxy models and for simple stellar populations of various metallicities. We show how the luminosity weighted stellar metallicity indicators in different wavelength bands from U to K compare to each other for the various star formation histories and how they evolve in time. We analyse as a function of wavelength the luminosity contributions of stellar subpopulations with different metallicities in the various galaxy types. The relations between luminosity weighted stellar metallicity indicators in different passbands, stellar absorption indices and ISM abundances are shown to depend significantly on the star formation history and evolutionary stage.