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

TL;DR

This study uses high-resolution simulations to show that cosmic rays significantly influence the size, survival, and mass of cold gas clouds in the circumgalactic medium, impacting galaxy feeding and star formation.

Contribution

It reveals how cosmic rays modify cold gas cloud properties and enhance cold gas inflow into galaxies, a novel insight into CGM physics.

Findings

CRs increase cold cloud mass by up to four times

CR pressure enhances cloud surface area and mixing-layer cooling

CRs lead to higher star formation rates at later times

Abstract

Does cosmic ray (CR) pressure matter for the circumgalactic medium (CGM)? Despite growing interest, this remains a debated question, complicated by limited observational constraints and differing implementations of CR physics in simulations. While prior studies suggest that CRs influence the thermal and dynamical state of the CGM, their role in shaping cold gas structures remains underexplored. This paper investigates 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 the cold clouds, increasing their surface area and enabling more efficient mixing-layer cooling, allowing them to grow in mass. This enhanced growth results in higher cold gas inflow rates into the central galaxy, leading to an increase in the star formation rate compared to the no-CR case at a later time. Moreover, CRs can boost the total cold gas mass in the CGM by up to a factor of four. These effects are most pronounced in simulations where the CR energy density is in equipartition with the thermal gas. Our results demonstrate 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.