Capturing a Star Formation Burst in Galaxies Infalling onto the Cluster A1367

The discovery of a striking astrophysical laboratory in the cluster ofgalaxies Abell 1367 (Sakai et al. 2002) is confirmed with independent imagingand spectroscopic observations and further investigated in the presentanalysis. Two giant and ten dwarf/HII galaxies, members to a group, aresimultaneously undergoing a burst of star formation. Redshift measurementssuggest that the group galaxies are in the process of falling into the clusterat very high speed. We explore two possible mechanisms that could havetriggered the short-lived stellar burst we are witnessing: the first, internalto the group itself, via tidal interactions among its members, the hypothesisfavoured by Sakai et al. (2002); the second associated with the high velocityinfall of the group galaxies into the cluster intergalactic medium. We presentevidences in favour and against the two hypotheses.