HIERARCHICAL GALAXY FORMATION - OVERMERGING AND THE FORMATION OF AN X-RAY-CLUSTER

We simulate the formation of a moderately rich cluster in a cold dark matter universe using a technique which allows us to follow both the dark matter and the baryonic gas. Gas is able to shock-beat, and to cool by Compton scattering and collisional radiation. Our initial condition is taken from a large dissipationless simulation carried out by White et al. (1987), and we are able to follow the evolution of the cluster in its proper cosmological context by using a multimass grid technique to represent the gravitational field of external matter. We take 9% of the mass to be in the form of gas. Just over one-third of this gas cools to form dense compact lumps as the cluster evolves. The abundance and mass of these lumps is consistent with the expected number and mass of galaxies in the cluster, but our numerical resolution permits us to see only the few most massive objects. The temperature distribution of the intracluster ps in our final object is far from isothermal and has a multiphase structure in its inner regions. Overall, however, the inferred X-ray surface brightness profile is quite similar to that of the Virgo Cluster.