To Survive or To Shatter: The Impact of Cosmic Rays on the Fate of Stripped Cold Clouds

Artikel i vetenskaplig tidskrift, 2026

Does cosmic-ray (CR) pressure matter for the circumgalactic medium (CGM)? While prior studies suggest that CRs influence the thermal and dynamical state of the CGM, their overall importance remains an open question due to limited observational constraints and the strong dependence of simulation predictions on the implementation of CR physics. In the context of the multiphase CGM, the role of CRs remains underexplored, especially in governing the formation and survival of cold gas clouds and structures that are expected to fuel future star formation in the host galaxy. We investigate how CRs affect ram-pressure-stripped cold gas clouds originating from satellite galaxies in a Milky Way–like halo. Using high-resolution simulations with varying CR energy densities, we find that CRs can significantly modify the size and survival of stripped clouds. Specifically, CR pressure “puffs up” cold clouds, increasing their surface area and enabling more efficient mixing-layer cooling, which allows them to grow in mass. This enhanced growth results in higher cold gas inflow rates into the central galaxy, leading to an increased star formation rate compared to the no-CR case at later times. Moreover, CRs can boost the total cold gas mass in the CGM by up to a factor of 4. These effects are most pronounced in simulations where the CR energy density is in equipartition with the thermal gas. We show that CRs can play a critical role in regulating the cold phase of the CGM contributed by satellites, and therefore their ability to feed galaxies.