Dwarf galaxies and the origin of the intracluster medium

Abstract

Following the recent suggestion that it is dwarf galaxies in clusters as opposed to large ellipticals that provide the intracluster gas, we estimate the metallicity of the intracluster medium in such a case. We derive analytical expressions for the fraction of mass of dwarf galaxies that is ejected and estimate the metallicity of the resulting intracluster gas. We find that the metallicity resulting from this hypothesis is adequate only for clusters with low-metallicity gas. Since galactic winds from dwarf galaxies occur much earlier than those from ellipticals, because of the smaller binding energy of the gas, we show that the gas ejected by dwarf galaxies is enriched mostly by Type II supernovae, as opposed to Type I supernovae in the case of large galaxies. We further point out that the gas in small-scale structures, which never cools and forms stars owing to low temperatures and, consequently, a large cooling timescale, gets dispersed in the process of hierarchical clustering and is incorporated as the diffuse intracluster gas. We show that this process can provide enough hot gas to be compatible with X-ray observations in rich clusters.