Formation of starburst galaxies in merging clusters

A significant fraction of clusters of galaxies are observed to have substru cture, which implies that merging between clusters and subclusters is a rat her common physical process in cluster formation. It still remains unclear how cluster merging affects the evolution of cluster member galaxies. We re port the results of numerical simulations that show the dynamical evolution of a gas-rich, late-type spiral in a merger between a small group of galax ies and a cluster. The simulations demonstrate that the time-dependent tida l gravitational field during merging excites non-axisymmetric structure of the galaxy, subsequently drives efficient transfer of gas to the central re gion and finally triggers a secondary starburst. This result provides a clo se physical relationship between the emergence of starburst galaxies and th e formation of substructure in clusters. We accordingly interpret post-star burst galaxies located near substructure of the Coma Cluster as one observa tional example indicating the global tidal effects of group-cluster merging . Our numerical results further suggest a causal link between the observed excess of blue galaxies in distant clusters and the cluster virialization p rocess through hierarchical merging of subclusters.