Hierarchical clustering and the baryon distribution in galaxy clusters

The baryon fraction of galaxy clusters in numerical simulations is found to be dependent on the cluster formation method. In all cases, the gas is antibiased compared with the dark matter. However, clusters formed hierarchically are found to be more depleted in baryons than clusters formed non-hierarchically. There is a depletion of 10 to 15 per cent for hierarchically formed clusters, while the depletion is less than 10 per cent for those clusters formed non-hierarchically. This difference is dependent on the mass of the clusters. The mean baryon enrichment profile for the hierarchically formed clusters shows an appreciable baryon enhancement around the virial radius not seen in the clusters formed without substructure. If this phenomenon applies to real clusters, it implies that determinations of the baryon fractions in clusters of galaxies require data extending beyond the virial radius of the clusters in order to achieve an unbiased value.