Probing the evolution of early-type cluster galaxies through chemical enrichment

Abstract

A simple chemical enrichment model for cluster early-type galaxies is described in which the mechanisms considered in the evolutionary model are infall of primordial gas, outflows and a possible variation in the star formation efficiency. We find that - within the framework of our models - only outflows can generate a suitable range of metallicities. The chemical enrichment tracks can be combined with the latest population synthesis models to simulate clusters over a wide redshift range, for a set of toy models. The color-magnitude relation of local clusters is used as a constraint, fixing the correlation between absolute luminosity and ejected fraction of gas from outflows. It is found that the correlations between color or mass-to-light ratios and absolute luminosity are degenerate with respect to most of the input parameters. However, a significant change between monolithic and hierarchical models is predicted for redshifts $z\simgt 1$. The comparison between predicted and observed mass-to-light ratios yield an approximate linear bias between total and stellar masses: $M_{\rm Tot}\propto M_{\rm St}^{1.15\pm 0.08}$ in early-type galaxies. If we assume that outflows constitute the driving mechanism for the colors observed in cluster early type galaxies, the metallicity of the intracluster medium (ICM) can be linked to outflows. The color-magnitude constraint requires faint $M_V\sim -16$ galaxies to eject 85% of their gas, which means that most of the metals in the ICM may have originated in these dwarf galaxies.