Title: Stellar Populations of Cluster E and S0 Galaxies
Author(s): Inger Jørgensen
Keywords: galaxies: elliptical and lenticular -- galaxies: stellar content -- galaxies: fundamental parameters -- galaxies: scaling laws
E-Mail: Inger Jørgensen (to request a full copy of this paper)
Preprint: 9702076 Document source or PostScript
Release date: 02/10/97 10:51:50
Publication status: accepted for publication in MNRAS
Comments: 29 pages, 14 figures
Spectral line index data for a sample of 290 E and S0 galaxies are used to investigate the stellar populations of these galaxies. 250 of the galaxies are members of 11 nearby clusters (czCMB > 11500km/s). It is studied how the stellar populations of the galaxies are related to the velocity dispersions, the masses of the galaxies, and the cluster environment. This is done by establishing relations between these parameters and the line indices Mg2, <Fe>, and Hbeta.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] is 0.3-0.4 dex higher for galaxies with velocity dispersions of 250km/s compared to galaxies with velocity dispersions of 100km/s. This is in agreement with previous estimates by Worthey et al.
The <Fe> index is stronger correlated with the projected cluster surface density, rhocluster, than with the galaxy mass or the velocity dispersion. We have earlier found the residuals for the Mg2-sigma relation to depend on the cluster environment. Here we determine how both the Mg2 index and the <Fe> index depend on the velocity disperson and rhocluster. Alternative explanations that could create a spurious environment dependence are discussed. No obvious alternatives are found. The environment dependence of the Mg2-sigma relation is supported by data from Faber et al. The dependence on the environment implies that [Mg/Fe] decreases with increasing density. The decrease in [Mg/Fe] is 0.1 dex over 2.5 dex in rhocluster.
We have also studied to what extend the mass-to-light (M/L) ratios of the galaxies are determined by the stellar populations. The M/L ratios are strongly correlated with the indices Mg2 and Hbeta, while the <Fe> index is only weakly correlated with the M/L ratio.
Based on current stellar population models we find that 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).