OMEGA–OSIRIS mapping of emission-line galaxies in A901/2–V : the rich population of jellyfish galaxies in the multicluster system Abell 901/2

Abstract

We present the results of a systematic search and characterization of galaxies with morphological signatures of ram pressure stripping, known as jellyfish galaxies, in the multicluster system A901/2, at z ~ 0.165, as part of the OMEGA survey. By visually inspecting Advanced Camera for Surveys/Hubble Space Telescope F606W images looking for morphological signatures of ram pressure stripping events in Hα-emitting galaxies, we identify a total of 70 jellyfish candidates. Of these, 53 are clearly star-forming galaxies and five are highly probable active galactic nucleus (AGN) hosts, the classification of the remaining galaxies is more uncertain. They have late-type and irregular morphologies, and most of them are part of the blue cloud with only. four being previously classified as dusty reds. The AGN activity is not prominent in the sample and, of the few cases of galaxies hosting AGN, such activity does not seem to be correlated to the gas-stripping phenomenon. Our jellyfish galaxy candidates do not have a preferential pattern of motion within the multicluster system, although the most compelling cases appear to inhabit the inner regions of the most massive sub-cluster centres. The specific star formation rate of these galaxies indicates that their star formation activity is enhanced, in contrast with what is observed for the rest of the star-forming galaxy population in the system. Half of the sample is forming stars at a higher rate than the main sequence for field galaxies, and this behaviour is more evident for the most compelling candidates. For some galaxies, the spatially resolved Hα emission appears to be as disturbed and extended as their continuum counterparts.Our findings point towards a scenario where the ram pressure stripping is triggering a period of intense and extended star formation throughout the galaxy while it is also disturbing the morphology. This is the largest sample of jellyfish galaxy candidates found in a single system suggesting that cluster mergers might be the ideal environment for studying ram pressure stripping effects.