Stellar Populations in Field Early-Type Galaxies

With the aim of understanding the role played by mass and environment on the evolution of early-type galaxies (ETGs), we are performing a multi-band study from ultraviolet (UV) to infrared (IR) of a sample 65 nearby ETGs. We derived Lick line-strength indices at different galacto-centric distances from the optical spectra (3700-7000 angstrom), and extracted ages, metallicites and element abundance ratios for the galaxies by comparison of the indices with new Simple Stellar Population (SSP) models. We then analyzed the behavior of the derived stellar population parameters with the central galaxy velocity dispersion and the local galaxy density. We find that the chemical path is mainly driven by the halo mass, more massive galaxies exhibiting the more efficient chemical enrichment and shorter star formation timescales. Galaxies in denser environments are on average older than galaxies in less dense environments. In particular, luminosity-weighted ages as young as few Gyrs are derived for some galaxies of the sample in the lowest density environments. We suggest that these objects are old galaxies that experienced secondary "rejuvenating" episodes of star formation. We discuss how we will constrain the mass involved in the rejuvenating episodes by complementing the optical spectra with new GALEX and Spitzer data.