The Launching of Cold Clouds by Galaxy Outflows. III. The Influence of Magnetic Fields

Motivated by observations of outflowing galaxies, we investigate the combined impact of magnetic fields and radiative cooling on the evolution of cold clouds embedded in a hot wind. We perform a collection of threedimensional adaptive mesh refinement, magnetohydrodynamical simulations that span two resolutions, and include fields that are aligned and transverse to the oncoming, super-Alfvenic material. Aligned fields have little impact on the overall lifetime of the clouds over the non-magnetized case, although they do increase the mixing between the wind and cloud material by a factor of ≈3. Transverse fields lead to magnetic draping, which isolates the clouds, but they also squeeze material in the direction perpendicular to the field lines, which leads to rapid mass loss. A resolution study suggests that the magnetized simulations have somewhat better convergence properties than nonmagnetized simulations, and that a resolution of 64 zones per cloud radius is sufficient to accurately describe these interactions. We conclude that the combined effects of radiative cooling and magnetic fields are dependent on field orientation, but are unlikely to enhance cloud lifetimes beyond the effect of radiative cooling alone.This work was supported by the National Science Foundation under grants OISE-1458445 and AST-1715876. MB is supported by a grant by the Deutsche Forschungsgemeinschaft under BR2026-12. WBB is supported by the Deutsche Forschungsgemeinschaft (DFG) via grant BR2026215. We would like to thank the Texas Advanced Computing Center (TACC) at The University of Texas at Austin, and the Extreme Science and Engineering Discovery Environment (XSEDE) for providing HPC resources via grants TGAST130021 and TG-AST160063 that have contributed to the results reported within this paper. The software used in this work was in part developed by the DOE-supported Flash Center for Computational Science at the University of Chicago. C.F. acknowledges funding provided by the Australian Research Council (Discovery Project DP170100603 and Future Fellowship FT180100495), and the Australia-Germany Joint Research Cooperation Scheme (UA-DAAD)