Stress-testing cosmic ray physics: the impact of cosmic rays on the surviving disc of ram-pressure-stripped galaxies

Abstract

ABSTRACT Cluster spiral galaxies suffer catastrophic losses of the cool, neutral gas component of their interstellar medium due to ram pressure stripping, contributing to the observed quenching of star formation in the disc compared to galaxies in lower density environments. However, the short-term effects of ram pressure on the star formation rate and active galactic nucleus (AGN) activity of galaxies undergoing stripping remain unclear. Numerical studies have recently demonstrated cosmic rays can dramatically influence galaxy evolution for isolated galaxies, yet their influence on ram pressure stripping remains poorly constrained. We perform the first cosmic ray magnetohydrodynamic simulations of an L* galaxy undergoing ram pressure stripping, including radiative cooling, self-gravity of the gas, star formation, and stellar feedback. We find the microscopic transport of cosmic rays plays a key role in modulating the star formation enhancement experienced by spirals at the outskirts of clusters compared to isolated spirals. Moreover, we find that galaxies undergoing ram pressure stripping exhibit enhanced gas accretion on to their centres, which may explain the prevalence of AGNs in these objects. In agreement with observations, we find cosmic rays significantly boost the global radio emission of cluster spirals. Although the gas removal rate is relatively insensitive to cosmic ray physics, we find that cosmic rays significantly modify the phase distribution of the remaining gas disc. These results suggest observations of galaxies undergoing ram pressure stripping may place novel constraints on cosmic ray calorimetry and transport.