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Witnessing galaxy preprocessing in the local Universe: the case of the starbursting group infalling into Abell1367

L.Cortese, G.Gavazzi, A.Boselli, P.Franzetti, R.Kennicutt, K.O'Neil, S.Sakai

We present a multiwavelength analysis of a compact group of galaxies infalling at high speed into the dynamically young cluster Abell 1367. Peculiar morphologies and unusually high Halpha emission are associated to two giant galaxies and at least ten dwarfs/extragalactic HII regions, making this group the region with the highest density of star formation activity ever observed in the local clusters. Moreover Halpha imaging observations reveal extraordinary complex trails of ionized gas behind galaxies with projected lengths exceeding 150 kpc. These unique cometary trails mark the gaseous trajectory of galaxies, witnessing their dive into the hot cluster intergalactic medium. Under the combined action of tidal forces among group members and of ram-pressure by the cluster ambient medium the group galaxies were fragmented and the ionized gas was blown out of them. The properties of this group suggest that environmental effects within infalling groups may have represented a preprocessing step in the galaxy evolution during cluster assembling at higher redshift.

The BIG Group images

Big_RGB Big_rBand Big_net Big_net
Fig1:The RGB image of the BIG group. Blue is Halpha Net band, Red is r' band and Green is Halpha on band. Fig2:Extended low surface brightness loops and trails appear in the Halpha+[NII] net frame around the giant and dwarf galaxies in BIG. Fig3:r' band frame. Stellar shells around the the bright early type spiral CGCG97-125 are clearly visible. Fig4:A stellar trail and diffuse intra-group light appear in the high contrast r' image of BIG.

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