Abstract
We examine the contributions of gas and galaxy mass to the total mass of clusters of galaxies as an indicator of the origin of the dark matter component in clusters and the mass density of the universe. First, we compare the observed X‐ray and optical relations in clusters to the results of large‐scale hydrodynamic simulations and show that low‐density CDM is more consistent with the observed gas mass fractions in clusters. Secondly, we examine the make‐up of the total cluster mass and suggest that there is no excess of dark matter in these systems; that is, their mass can be accounted for by the mass of the member galaxies (including their dark halos) and the mass of the baryonic intracluster gas. This would imply that the fractional contribution of the dark matter component does not keep increasing with scale beyond the very large halos suggested for individual galaxies and that the mass density of the universe is of the order of the mass density observed on the scale of clusters, i.e., Ω∼0.2.
Published Version
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