Capturing a star formation burst in galaxies infalling onto the cluster A1367

The discovery of a striking astrophysical laboratory in the cluster of galaxies A1367 by Sakai and coworkers is confirmed with independent imaging and spectroscopic observations and further investigated in the present analysis. Two giant and 10 dwarf/ H II galaxies, members of a group, are simultaneously undergoing a burst of star formation. Redshift measurements suggest that the group galaxies are in the process of falling into the cluster at very high speed. We explore two possible mechanisms that could have triggered the short-lived stellar burst that we are witnessing: the first, internal to the group itself, via tidal interactions among its members, the hypothesis favored by Sakai et al.; the second associated with the high-velocity infall of the group galaxies into the cluster intergalactic medium. We present evidence in favor of and against the two hypotheses.