Metallicity of Dwarf Galaxies in Clusters

Abstract

Dwarf galaxies in clusters seem to follow only loosely the correlation between metallicity and luminosity that has been well established for isolated dwarf galaxies up to massive galaxies. Several studies indicate that they have oxygen abundances higher than expected, e.g. in the Hydra I cluster where we have measured the metallicity of a complete sample of HI-rich dwarf galaxies (Duc et al. 1999). These results indicate that the environment might affect the chemical evolution of galaxies. Among the possible mechanisms are the confinement of heavy elements by the intracluster medium or the reprocessing of pre-enriched material expelled from disk galaxies, either via ram-pressure by the intra-cluster medium or via galaxy collisions. The latter phenomena is at the origin of the so-called tidal dwarf galaxies, objects originally found in the tidal tails of interacting galaxies but that may escape their parent galaxies and populate clusters. Their rather uniform metallicity of 1/3^rd of solar (see Fig. 1 and Duc & Mirabel, 1998) reflects that of spiral disks at R ₂₅.