Are we missing baryons in Galaxy Clusters?

Abstract

The recent constraints on the cosmological parameters put from the observations of the WMAP satellite limit the cosmic baryon fraction in a range that is larger than, and marginally consistent with, what is measured in galaxy clusters. This rises the question whether or not we are considering all the ingredients of cluster baryonic budget. Making a careful weight of the baryons in X-ray emitting plasma and stars in cluster galaxies, I conclude that the cluster baryonic pie is made by 13 (with a 1 sigma range of 8-19) per cent of stars, 70 (56-89) per cent of intracluster hot medium and 17 (0-33) per cent, and a probability of 73 per cent to be larger than 0, of ``other'' baryons, presumably in the form of warm (1e5-1e7 Kelvin) material.