A search for environmentally driven star formation in nearby galaxy clusters

An observational study of the effect of the dynamical state of a galaxy cluster on the rate of current star formation in cluster galaxies is presented. Study of a set of clusters with different dynamical states shows that while most cluster galaxies have star formation properties indistinguishable from field galaxies, some galaxies in relaxed clusters have depressed star formation, while some in unrelaxed clusters have enhanced star formation.; A complete survey of the dynamically unrelaxed Hercules cluster shows that the galaxies with excess star formation do not associate themselves preferentially with any of the existing substructure in the cluster. The most likely mechanism for triggering the excess star formation in the Hercules cluster is interactions or mergers with small galaxies as the galaxies fall into the cluster for the first time.