Zooming in on the Circumgalactic Medium with GIBLE: the Topology and Draping of Magnetic Fields around Cold Clouds

Abstract

We use a cosmological zoom-in simulation of a Milky Way-like galaxy to study and quantify the topology of magnetic field lines around cold gas clouds in the circumgalactic medium (CGM). This simulation is a new addition to Project GIBLE, a suite of cosmological magnetohydrodynamical simulations of galaxy formation with preferential super-Lagrangian refinement in the CGM, reaching an unprecedented (CGM) gas mass resolution of $\sim$ $225$ M$_\odot$. To maximize statistics and resolution, we focus on a sample of $\sim$ $200$ clouds with masses of $\sim$ $10^6$ M$_\odot$. The topology of magnetic field lines around clouds is diverse, from threading to draping, and there is large variation in the magnetic curvature ($κ$) within cloud-background interfaces. We typically find little variation of $κ$ between upstream and downstream cloud faces, implying that strongly draped configurations are rare. In addition, $κ$ correlates strongly with multiple properties of the interface and the ambient background, including cloud overdensity and relative velocity, suggesting that cloud properties impact the topology of interface magnetic fields.