Formation of Groups and Clusters of Galaxies

The formation, inner properties, and spatial distribution of galaxy groups and clusters are closely related to the background cosmological model. We use numerical simulations of variants of the CDM model with different cosmological parameters and distinguish relaxed objects from recent mergers using the degree of virialisation. Mergers occur mostly in deep potential wells and mark the most important structure formation processes. As consequence, the autocorrelation function of merged halos has a higher amplitude and is steeper than that of the virialized clusters. This can be directly connected to the same result found from the observation of luminous infrared galaxies; they are as well more strongly correlated and can primarily be identified with ongoing merging events.