The stellar populations of early-type galaxies in the Fornax cluster

Abstract

We have measured central line strengths for a magnitude-limited sample of early-type galaxies in the Fornax cluster, comprising 11 elliptical (E) and 11 lenticular (S0) galaxies, more luminous than MB=-17. When compared with single-burst stellar population models we find that the centres of Fornax ellipticals follow a locus of fixed age and have metallicities varying roughly from half solar to two times solar. The centres of (lower luminosity) lenticular galaxies, however, exhibit a substantial spread to younger luminosity-weighted ages indicating a more extended star formation history. Galaxies with old stellar populations show tight scaling relations between metal-line indices and the central velocity dispersion. Remarkably also the Fe-lines are well correlated with sigma. Our detailed analysis of the stellar populations suggests that these scaling relations are driven mostly by metallicity. Galaxies with a young stellar component do generally deviate from the main relation. In particular the lower luminosity S0s show a large spread. Furthermore we find that elliptical galaxies and the bulge of one bright S0 are overabundant in magnesium, where the most luminous galaxies show the strongest overabundances. The stellar populations of young and faint S0s are consistent with solar abundance ratios or a weak Mg underabundance. (abriged)