Capturing a star formation burst in galaxies infalling onto the cluster Abell 1367

G.Gavazzi, L.Cortese, A.Boselli, J.Iglesias-Paramo, J.M.Vilchez & L.Carrasco

The discovery of a striking astrophysical laboratory in the cluster of galaxies Abell 1367 (Sakai et al. 2002) is confirmed with independent imaging and spectroscopic observations and further investigated in the present analysis. Two giant and ten dwarf HII galaxies, members to 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 we are witnessing: the first, internal to the group itself, via tidal interactions among its members, the hypothesis favoured by Sakai et al. (2002); the second associated with the high velocity infall of the group galaxies into the cluster intergalactic medium. We present evidences in favour and against the two hypotheses.

The BIG Group images

Big_RGB Big_rBand Big_net
Fig1:The 5x5 arcmin field centered on the group of galaxies projected near the X-ray centre of Abell 1367. Blue color corresponds to the H_alpha emission. Fig2:High-contrast r' Band frame of the BIG group Fig3:Net (H_alpha + N[II]) Band frame of the BIG group

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