Letter to the Editor

Zooming in on the circumgalactic medium with GIBLE

The topology and draping of magnetic fields around cold clouds

¹ Universität Heidelberg, Zentrum für Astronomie, ITA, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
e-mail: rahul.ramesh@stud.uni-heidelberg.de
² Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
³ Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
⁴ Hamburg University, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received: 29 November 2023
Accepted: 27 March 2024

Abstract

We used 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 magnetohydrodynamic simulations of galaxy formation with preferential super-Lagrangian refinement in the CGM, reaching an unprecedented CGM gas mass resolution of ∼225 M_⊙. To maximize statistics and resolution, we focused on a sample of ∼200 clouds with masses of ∼10⁶ M_⊙. 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.