Asger Grønnow - Magnetised clouds in the Galactic corona

Abstract: The Galactic halo contains a complex ecosystem of multiphase intermediate-velocity and high-velocity gas clouds whose origin has defied clear explanation. They are generally believed to be involved in a Galaxy-wide recycling process, either through an accretion flow or a large-scale fountain flow, or both. Recent numerical studies have found that they accrete gas efficiently from the hot corona as they move through it. In these models, gas stripped from the clouds mixes with the low density coronal gas significantly reducing its cooling time scale. The newly cooled gas rains down on the disk where it is accreted and may fuel star formation. These studies, however, ignore the effects of the coronal magnetic field and are typically two-dimensional. In this talk, I will present our 3D high-resolution simulations where we find that the magnetic field significantly decreases the amount of mixing by damping instability along the cloud boundaries. This in turn suppresses the condensation in the wake of clouds, preventing the sharp upturn in cold gas seen in previous non-magnetic studies and significantly lowering the efficiency of fountain-driven accretion. These lower accretion rates are in better agreement with observational constraints.