No Evidence of Asymmetrically Enhanced Star Formation in Infalling Galaxies in UNIONS

Abstract Ram pressure stripping is a well-known environmental quenching mechanism that removes gas from galaxies infalling into groups and clusters. In some extreme examples of ram pressure stripping, galaxies with extended gas tails show evidence of enhanced star formation prior to quenching. In this work we use a sample of 5277 local satellite galaxies in which a stripped tail of gas has not necessarily been observed, to quantify the strength of ram-pressure-enhanced star formation and compare these results to a control sample of 8360 field galaxies. We use u -band imaging from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS) as a star formation tracer and several metrics to quantify star formation asymmetry. We compare these results to environmental properties of the galaxy, such as their time since infall and host halo mass, to constrain the degree of ram-pressure-enhanced star formation as a function of environment. We find no significant differences between the satellite and the field samples. We further restrict our sample to galaxies which we most expect to be experiencing significant ram pressure but find no strong evidence of these galaxies having systematically enhanced star formation. Finally, we investigate the properties of the most asymmetric galaxies in our sample and again find no strong evidence of ram-pressure-induced star formation enhancement. We conclude that any star formation enhancement must be small for infalling galaxies, suggesting that this effect is either uncommon or short-lived.