Ram pressure candidates in UNIONS

Abstract

We present a search for disturbed, candidate ram pressure stripping galaxies across more than 50 spectroscopically selected SDSS groups and clusters. 48 ram pressure candidates are visually identified in these systems using high-quality UNIONS imaging from the Canada-France-Hawaii Telescope, covering ${\sim }6200\, \mathrm{deg^2}$ and ${\sim }2800\, \mathrm{deg^2}$ in the u- and r-bands, respectively. Ram pressure candidates are found in groups and clusters spanning a wide range in halo mass and include ∼30 ram pressure candidates in the group regime (Mh < 1014). The observed frequency of ram pressure candidates shows substantial scatter with group/cluster mass, but on average is larger in clusters ($M_h \ge 10^{14}\, \mathrm{M_\odot }$) than groups ($M_h \lt 10^{14}\, \mathrm{M_\odot }$) by a factor of ∼2. We find that ram pressure candidates are most commonly low-mass galaxies and have enhanced star formation rates relative to star-forming field galaxies. The enhancement in star formation is largely independent of galaxy mass and strongest for galaxies in clusters. As a result of the large survey footprint and excellent image quality from UNIONS, we are able to identify disturbed galaxies, potentially affected by ram pressure stripping, across a wide range of host environment.

Ram pressure stripping in the z~0.5 galaxy cluster MS 0451.6-0305

“…Among the two clusters, MS0451 star-forming RPS galaxies show increased levels of SF activity, lying mostly above the MS. We can only conjecture that this is due to the different dynamical states of the clusters. The enhanced median values of SFRs and sSFRs of our RPS candidates agree with those already found by previous authors such as Durret et al (2021), Roberts et al (2022) and references therein.…”

“…Vulcani et al (2018) found a similar result when comparing 42 RPS cluster galaxies to a control sample of 32 galaxies (field and undisturbed galaxies) from the GASP survey, all with stellar masses above 10 9 M . Roberts et al (2022) observed a large sample of isolated field galaxies at low redshift and found that 77% of their RPS galaxies (stellar masses above 10 8.8 M ) lie above the star-forming main sequence drawn in their Figure 8. The general assessment thus seems to be that environment, particular RPS, is indeed triggering episodes of enhanced SFR at various redshifts.…”

Ram pressure stripping in the z ∼ 0.5 galaxy cluster MS 0451.6-0305

“…KS tests confirm that all these samples are likely drawn from different populations, so the above inferences should hold, and RPS galaxies appear to have, in general, lower masses than non-RPS galaxies. Although uncertainties in the mass determination are large, the trend we find agrees with what is observed in the local Universe across groups and clusters, as probed at z <0.04 in the SDSS-UNIONS survey by Roberts et al (2022): RPS candidates commonly seem to be low-mass galaxies.…”

“…This different behaviour for the different mass regimes of RPS candidates was not detected in low-z clusters (e.g. Poggianti et al 2016) nor in the field (Roberts et al 2022) and will definitely need to be confirmed -or not -with a deeper and more complete set of spectroscopic data. If true, it might be linked to the specific dynamical conditions of this post-merging cluster.…”

“…Vulcani et al (2018) found a similar result when comparing 42 RPS cluster galaxies to a control sample of 32 galaxies (field and undisturbed galaxies) from the GASP survey, all with stellar masses above 10 9 M . Roberts et al (2022) observed a large sample of isolated field galaxies at low redshift and found that 77% of their RPS galaxies (stellar masses above 10 8.8 M ) lie above the star-forming main sequence drawn in their Fig. 8.…”