Abstract
We present the results of a systematic search and characterisation of jellyfish galaxy candidates in the multi-cluster system A901/2, at z ~ 0.165, as part of the OMEGA survey. By visual inspecting ACS/HST F606W images looking for morphological signatures of ram-pressure stripping events in Halpha-emitting galaxies, we identify a total of 70 candidates. Out of these, 53 are clearly star-forming galaxies and 5 are highly probable 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 4 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 multi-cluster system, although the most compelling cases appear to inhabit the inner regions of the most massive sub-cluster centres. The sSFR 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 Halpha 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.
Highlights
The environment in which galaxies inhabit influences their physical properties and evolution
Stellar mass distribution and SED types to find whether the jellyfish phenomenon is associated to galaxies with distinct properties
One reason why we may not detect many dusty reds as jellyfish galaxies might be due to the fact that these galaxies, despite having relatively high SFRs, have significant levels of obscuration by dust which might hamper the identification of the jellyfish signatures
Summary
The environment in which galaxies inhabit influences their physical properties and evolution. The jellyfish morphology appears to resemble that of tadpole galaxies, objects first found in the higher redshift Universe probed by the Hubble Deep Field (HDF) (van den Bergh et al 1996) and later studied in more detail in the Hubble Ultra Deep Field (HUDF) (Elmegreen et al 2007; Elmegreen & Elmegreen 2010; Straughn et al 2015) These are galaxies with a diffuse tail attached to a head of a bright decentralised clumpy star-forming structure (Sanchez Almeida et al 2013).
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