Magnetic fields in the intracluster medium with TNG-Cluster: Properties, morphology, and tangential anisotropy

¹ Universität Heidelberg, Zentrum für Astronomie, ITA, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
² Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
³ Universität Heidelberg, Interdisziplinäres Zentrum für Wissenschaftliches Rechnen, INF 205, 69120 Heidelberg, Germany
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Département de Physique, Université de Montréal, Succ. Centre-Ville, Montréal, Québec H3C 3J7, Canada
⁶ Centre de recherche en astrophysique du Quebec (CRAQ), Montréal, Québec H3C 3J7, Canada

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 July 2025
Accepted: 9 November 2025

Abstract

We characterized the magnetic field properties of 352 massive galaxy clusters from the TNG-Cluster magnetohydrodynamical (MHD) cosmological simulation with a focus on central magnetic field morphology in cool-core (CC) versus non-cool-core (NCC) clusters. We present the central values and radial profiles of magnetic field strength and plasma parameter as a function of mass, cooling status, and redshift. Compared to low-redshift observations, TNG-Cluster produces reasonable magnetic field amplitudes in the central regions of clusters, spanning a range of 1 − 200 μG. In this paper, we discuss the main finding of this work, namely, that z = 0 CC clusters have preferentially tangential magnetic fields at a characteristic scale of ∼0.1r_500c. These strongly tangential field orientations are specific to CCs. In contrast, across the full cluster population, magnetic fields show isotropic configurations at all radii and redshifts. As individual halos grow, the evolution of their magnetic field topologies is diverse: tangential features can be short-lived, persist over large cosmological time-scales, or periodically appear, vanish, and reappear towards z = 0. We discuss the underlying physics and possible physical scenarios to explain the origin of these structures. We argue that both short-term active galactic nucleus (AGN) feedback-driven outflows and merger-driven sloshing motions, cannot explain the population-wide tangential bias in magnetic field orientation. Instead, we propose that the trapping of internal gravity waves is responsible for the tangentially biased magnetic field topologies that we find in CC TNG-Cluster halos, due to the strong entropy gradient in these clusters.