LoTSS jellyfish galaxies: I. Radio tails in low redshift clusters

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 L 144MHz − 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.

LoTSS jellyfish galaxies: II. Ram pressure stripping in groups versus clusters

“…That said, there has been very little work probing the SFRs of galaxies undergoing RPS in lower mass groups. The results of this work are qualitatively consistent with Roberts et al (2021a), who show that ram pressure candidate galaxies in groups (identified from rest-frame optical imaging) have SFRs which are only marginally enhanced compared to much clearer SFR enhancements for the ram pressure candidates in their sample hosted by clusters. The origin of this difference between groups and clusters is not immediately clear, although as previously mentioned, it is possible that the more intense ram pressure in clusters can more strongly perturb the ISM in galaxies, leading to enhanced gas densities and increased star formation.…”

“…3 are consistent with previous works finding a higher fraction of galaxies undergoing RPS in more massive halos. For ram pressure candidates identified from rest-frame optical imaging, Roberts et al (2021a) find a factor of two increase in the frequency of ram pressure candidates from groups to clusters, and in the Illustris simulation, Yun et al (2019) find a similar halo mass trend for simulated jellyfish galaxies. While the methodologies for identifying RPS galaxies in these studies differ from this work, the qualitative trends between lower mass groups and massive galaxy clusters are consistent throughout.…”

“…These previous works show that RPS occurs in at least some galaxy groups, though the small number of galaxies identified thus far make it difficult to contrast the prevalence and effectiveness of RPS in groups versus clusters. Recently, Roberts et al (2021a) have performed a search for ram pressure candidates in SDSS groups and clusters with optical imaging from the Canada-France Imaging Survey (Ibata et al 2017). Roberts et al (2021a) identify ∼ 30 ram pressure candidates galaxies in groups (M halo < 10 14 M ), but there still remain uncertainties related to the accuracy of ram pressure identifications from optical imaging alone, given that the stellar disk may not always be strongly perturbed by ram pressure.…”

“…Recently, Roberts et al (2021a) have performed a search for ram pressure candidates in SDSS groups and clusters with optical imaging from the Canada-France Imaging Survey (Ibata et al 2017). Roberts et al (2021a) identify ∼ 30 ram pressure candidates galaxies in groups (M halo < 10 14 M ), but there still remain uncertainties related to the accuracy of ram pressure identifications from optical imaging alone, given that the stellar disk may not always be strongly perturbed by ram pressure. In Roberts et al (2021b) (hereafter R21b) we presented a sample of ∼100 jellyfish galaxies in nearby (z < 0.05) galaxy clusters, identified from 144 MHz radio continuum tails in the LOFAR Two-metre Sky Survey (LoTSS, Shimwell et al 2017.…”

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 synchrotronemitting 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 et al 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).…”