LoTSS jellyfish galaxies

II. Ram pressure stripping in groups versus clusters

¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA, Leiden, The Netherlands
e-mail: iroberts@strw.leidenuniv.nl
² University of Birmingham School of Physics and Astronomy, Edgbaston, Birmingham, UK
³ INAF – Osservatorio astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy

Received: 19 April 2021
Accepted: 10 June 2021

Abstract

Ram pressure stripping is a frequently cited mechanism for quenching galaxy star formation in dense environments. Numerous examples of ram pressure stripping in galaxy clusters are present in literature; however, substantially less work has been focused on ram pressure stripping in lower-mass groups, the most common galaxy environment in the local Universe. In this work we use the LOFAR Two-metre Sky Survey (LoTSS) to search for jellyfish galaxies (i.e., galaxies with ram pressure stripped tails extending beyond the optical disk) in ∼500 SDSS groups (z < 0.05), making this the most comprehensive search for ram pressure stripping in groups to date. We identify 60 jellyfish galaxies in groups with extended, asymmetric radio continuum tails, which are found across the entire range of group mass from 10^12.5 < M_group < 10¹⁴ h⁻¹ M_⊙. We compare the group jellyfish galaxies identified in this work with the LoTSS jellyfish galaxies in clusters presented in a recent work, allowing us to compare the effects of ram pressure stripping across three decades in group and cluster mass. We find that jellyfish galaxies are most commonly found in clusters, with the frequency decreasing towards the lowest-mass groups. Both the orientation of observed radio continuum tails and the positions of group jellyfish galaxies in phase space suggest that galaxies are stripped more slowly in groups relative to clusters. Finally, we find that the star formation rates of jellyfish galaxies in groups are consistent with ‘normal’ star-forming group galaxies, which is in contrast to cluster jellyfish galaxies that have clearly enhanced star formation rates. On the whole, there is clear evidence for ongoing ram pressure stripping in galaxy groups (down to very low group masses), though the frequency of jellyfish galaxies and the strength of ram pressure stripping appear lower in groups than in clusters. Differences in the efficiency of ram pressure stripping in groups versus clusters likely contribute to the positive trend between the quenched fraction and host halo mass observed in the local Universe.