The Calm Before the Storm: The Impact of Radiative Cooling on Magnetic Field Amplification

Abstract Turbulent radiative mixing layers (TRMLs) may play a crucial role in driving multiphase gas formation in galactic outflows and the circumgalactic medium. Magnetic fields pervade these regions and can be amplified by shear-driven turbulence and cooling-induced compression. However, strong magnetic fields inhibit mixing. We present three-dimensional magnetohydrodynamic simulations of ∼transonic, TRMLs, beginning with a weak uniform magnetic field (10 −12 G). Adiabatic simulations show essentially no change in magnetic-field strength during the first Kelvin–Helmholtz time, as one would expect. In contrast, simulations with radiative cooling boost the magnetic-field strength by a factor of 3–10. Allowing cooling to molecular temperatures appears to promote a sustained enhancement of magnetic-field strength, which may be aided by turbulent mixing. Our work helps to disentangle the driving mechanisms of magnetic-field amplification in turbulent mixing layers, which impact the survival of cold gas clouds in galactic winds.