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 describ e the time evolution of broad band colors U to K and metal indices (Fe 5335, Fe5270, Mg-2, Mgb), taking into account the increasing initial m etallicities of successive generations of stars. Using specific star f ormation prescriptions for the different spectral types of galaxies, w e show our model galaxy broad band colors, synthetic spectra, and ISM abundances are in agreement with observations of nearby samples and te mplate galaxies of the respective spectral types. We compare our synth etic Mg-2 indices with observations and study the time evolution of th e stellar index [MEFe] for composite elliptical galaxy models and for simple stellar populations of various metallicities. We show how the l uminosity weighted stellar metallicity indicators in different wavelen gth bands from U to K compare to each other for the various star forma tion histories and how they evolve in time. We analyse as a function o f wavelength the luminosity contributions of stellar subpopulations wi th different metallicities in the various galaxy types. The relations between luminosity weighted stellar metallicity indicators in differen t passbands, stellar absorption indices and ISM abundances are shown t o depend significantly on the star formation history and evolutionary stage.