LoTSS jellyfish galaxies

Abstract

Context. The cluster environment has a strong impact on galaxy star formation, as seen by the fact that clusters host proportionally more red, passive galaxies relative to the field. Ram pressure stripping may drive this environmental quenching by directly stripping cold gas from galactic disks. In some cases, ram pressure stripping gives rise to ‘jellyfish galaxies’, observed with clear ‘tentacles’ of stripped gas extending beyond the optical extent of the galaxy. Aims. In this paper we present a large sample of jellyfish galaxies in low redshift clusters (z < 0.05), identified through 120−168 MHz radio continuum from the LOFAR Two-metre Sky Survey (LoTSS). Methods. From a parent sample of 29 X-ray-detected SDSS galaxy clusters and their spectroscopic members, we visually identify 95 star-forming, LoTSS jellyfish galaxies with 144 MHz radio tails. Star formation rates (SFRs) and stellar masses are obtained for all galaxies from SED fits. For each jellyfish galaxy we determine the tail orientation with respect to the cluster centre and quantify the prominence of the radio tails with the 144 MHz shape asymmetry. Results. After carefully accounting for redshift-dependent selection effects, we find that the frequency of jellyfish galaxies is relatively constant from cluster to cluster. LoTSS jellyfish galaxies are preferentially found at small clustercentric radius and large velocity offsets within their host clusters and have radio tails that are oriented away from the cluster centre. These galaxies also show enhanced star formation, relative to both ‘normal’ cluster galaxies and isolated field galaxies, but generally fall within the scatter of the L144 MHz − SFR relation. Conclusions. The properties of the LoTSS jellyfish galaxies identified in this work are fully consistent with expectations from ram pressure stripping. This large sample of jellyfish galaxies will be valuable for further constraining ram pressure stripping and star formation quenching in nearby galaxy clusters. We show that LOFAR is a powerful instrument for identifying ram pressure stripped galaxies across extremely wide fields. Moving forward, we will push the search for jellyfish galaxies beyond this initial cluster sample, including a comprehensive survey of the galaxy group regime.

Clusters’ far-reaching influence on narrow-angle tail radio galaxies

“…Nowhere is this interaction more dramatically demonstrated than in radio galaxies moving through the ICM of their surrounding cluster. The synchrotron-emitting plasma that comprises the radio lobes is ejected from the body of the galaxy, meaning that it is subject to the hydrodynamical processes that result from its interaction with the ICM: ram pressure will cause the jets to bend (Cowie & McKee 1975;Begelman, Rees & Blandford 1979;O'Dea 1985;Roberts et al 2021), while buoyancy effects can cause them to 'float' towards the edge of the cluster (Gull & Northover 1973;Gendron-Marsolais et al 2017).…”

The relevance of ram pressure stripping for the evolution of blue cluster galaxies as seen at optical wavelengths

“…To have a complete picture, we have also performed a systematic search of galaxies showing unwinding features in local massive clusters, under the assumption that these can in some cases be produced by ram pressure stripping, complementing previous searches of galaxies with unilateral stripped debries. This assumption is supported both by observational studies (Bellhouse et al 2017(Bellhouse et al , 2019(Bellhouse et al , 2021 and by theoretical expectations (Schulz & Struck 2001;Roediger et al 2014;Steinhauser et al 2016), but previous visual identification efforts aimed at selecting ram pressure stripped can-didates did not take this category of galaxies in consideration (P16, Roberts et al 2021a;Durret et al 2021).…”

“…For galaxies experiencing strong ram pressure, these cosmic rays can be stripped out of the galaxy and detected as ram pressure stripped tails in the radio continuum (e.g., Gavazzi et al 1987;Murphy et al 2009;Chen et al 2020), giving reliable identifications of jellyfish galaxies. Roberts et al (2021a) used the LOFAR Two-metre Sky Survey (LoTSS) to search for jellyfish galaxies at 120-168 MHz radio wavelengths. They find that the frequency of ram pressure stripped galaxies among star-forming galaxies (sS-FRs > 10 −11 yr −1 ) is relatively constant from cluster to cluster and that ram pressure stripped galaxies are preferentially found at small clustercentric radius and large velocity offsets within their host clusters.…”

“…Subsequently, other groups have provided quite large catalogs of ram pressure stripped candidates, based on different wavelengths and identification techniques (e.g., Roberts et al 2020Roberts et al , 2021aDurret et al 2021). Roberts et al (2021b,c) showed how ram pressure stripped galaxies with long radio continuum tails are most commonly found in clusters, with the frequency decreasing towards the lowest-mass groups.…”

MUSE sneaks a peek at extreme ram-pressure stripping events -- V. Towards a complete view of the galaxy cluster A1367

“…Differently from isolated galaxies, where only internal processes determine their evolution, galaxies in dense environments are potentially subject to a large number of physical processes. These can be divided in two Saikia 1991; Roberts et al 2021), and from the analysis of molecular lines (e.g. Boselli et al 1994;Salomé et al 2006;Scott et al 2013;Jáchym et al 2014;Scott et al 2015).…”