Chemical evolution and star formation history in the local universe

We analyse galaxies from the Sloan Digital Sky Survey with our spectral synthesis code STARLIGHT. STARLIGHT finds the combination of simple stellar populations of different ages and metallicities that the best fits a galaxy spectrum. This allows us to derive several galaxy properties, such as mass in stars, star formation history and chemical evolution. From the residual spectrum (obtained by subtracting the modelled from the observed spectrum), we measure emission lines, from which we obtain properties of the gas inside galaxies. We study the evolution of star-forming galaxies. We find that the more massive galaxies have formed stars faster and enriched their gas more quickly. The evolution of stellar metallicity is directly studied. We calibrate the current star-formation rate derived from the synthesis with the one from H∝ luminosity. We derive the stellar mass-stellar metallicity relation (M*-Z*) for different redshifts. This was the first time the evolution of M*-Z* relation was derived for the same set of galaxies. We find that the metallicity evolution is compatible with that expected from a simple closed box chemical evolution model. For galaxies classified as LINERs, we show that their observed H∝ luminosity is compatible with the number of ionizing photons emitted by old stellar populations. This result implies a deep review of the rate of nuclear activity in galaxies in the local Universe.