A census of the ages and stellar metallicities of nearby galaxiesAnna Gallazzi
We have developed a new method, based on a recent, medium-high resolution population synthesis code, to derive simultaneous estimates of stellar metallicities, ages and stellar masses from galaxy optical spectra. The method has been successfully applied to a sample of nearly 200,000 galaxies from the Sloan Digital Sky Survey (SDSS), including both quiescent early-type and actively star-forming galaxies. The new age and stellar metallicity estimates, combined with the large statistical power of the SDSS, allows us to explore in great details the dependence of age and stellar metallicity on stellar mass for different classes of galaxies. We explore the implications of such relations for well-known scaling relations obeyed by early-type galaxies, such as the color-magnitude and the $Mg_2-\sigma_V$ relations. This allows us to quantify the relative role of metallicity and age in shaping the two relations. Finally we exploit the new physical parameters estimates to derive the total metal content in stars in the local Universe and to study the distribution of metals as a function of galaxy properties.