Stellar populations of cluster E and S0 galaxies

Abstract

Spectral line indices for a sample of 290 nearby E and S0 galaxies are used to investigate the stellar populations of these galaxies. Relations are established between the line indices (Mg2, <Fe>, Hbeta) and the velocity dispersions, the masses of the galaxies, the M/L ratios and the cluster environment. The difference between the slope of the Mg2-sigma relation and the slope of the <Fe>-sigma relation indicates that the abundance ratio [Mg/Fe] increases with the velocity dispersion. The <Fe> index is stronger correlated with the projected cluster surface density, than with the galaxy mass or the velocity dispersion. Also the Mg2 index depends on the cluster environment. The dependence on the environment implies that [Mg/Fe] decreases with increasing density. The M/L ratios are strongly correlated with the Mg2 and Hbeta, while <Fe> is only weakly correlated with the M/L ratio. Based on current stellar population models it is not yet possible to derive unique physical parameters (mean age, mean abundances, mean IMF, and fraction of dark matter) from the observables (line indices, velocity dispersion, mass, M/L ratio).