Nearby early-type galaxies with ionized gas. Characterization of the underlying stellar population

Abstract

We present a preliminary analysis of the sample of early type galaxies of Rampazzo et al. (2005), selected to build a data-set of spectral properties of well studied early-type galaxies showing emission lines. Because of the presence of emission lines, the sample is biased toward objects that might be expected to have ongoing and recent star formation. We have compared the line-strength indices presented in Rampazzo et al. (2005) with Simple Stellar Populations (SSPs) in order to characterize the underlying stellar population of the galaxies. We have derived ages, metallicities and [alpha/Fe] ratios. The positive trend of the sigma-metallicity and sigma-[alpha/Fe] relations is reproduced. The bulk of the galaxies span a range in metallicity from ~ solar to ~ twice solar and a range in [alpha/Fe] from ~0.2 to ~0.4. Furthermore the comparison of the derived parameters at different galactocentric distances shows the presence of negative metallicity gradients from the center outwards.