Witnessing galaxy preprocessing in the local Universe: the case of a star-bursting group falling into Abell 1367

摘要

We present a multiwavelength analysis of a compact group of galaxiesinfalling at high speed into the dynamically young cluster Abell 1367. Peculiarmorphologies and unusually high Halpha emission are associated with two giantgalaxies and at least ten dwarfs/extragalactic HII regions, making this groupthe region with the highest density of star formation activity ever observed inthe local clusters. Moreover Halpha imaging observations reveal extraordinarycomplex trails of ionized gas behind the galaxies, with projected lengthsexceeding 150 kpc. These unique cometary trails mark the gaseous trajectory ofgalaxies, witnessing their dive into the hot cluster intergalactic medium.Under the combined action of tidal forces among group members and theram-pressure by the cluster ambient medium, the group galaxies were fragmentedand the ionized gas was blown out. The properties of this group suggest thatenvironmental effects within infalling groups may have represented apreprocessing step of the galaxy evolution during the high redshift clusterassembly phase.