Ram Pressure Candidates in UNIONS

TL;DR

This study identifies and analyzes galaxies undergoing ram pressure stripping in over 50 SDSS groups and clusters, revealing their distribution, properties, and increased star formation activity, especially in cluster environments.

Contribution

It provides the first large-scale visual identification of ram pressure candidates across diverse environments using high-quality UNIONS imaging.

Findings

Ram pressure candidates are more common in clusters than in groups.

Most candidates are low-mass galaxies with enhanced star formation.

Star formation enhancement is strongest in cluster environments.

Abstract

We present a search for disturbed, candidate ram pressure stripping galaxies across more than 50 spectroscopically selected SDSS groups and clusters. Forty-eight ram pressure candidates are visually identified in these systems using high quality UNIONS imaging from the Canada-France Hawaii Telescope, covering ~6200 and ~2800 square degrees 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 ($M_h < 10^{14}$). The observed frequency of ram pressure candidates shows substantial scatter with group/cluster mass, but on average is larger in clusters ($M_h > 10^{14}\,M_\odot$) than groups ($M_h < 10^{14}\,M_\odot$) 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.