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

TL;DR

This study uses the TNG-Cluster simulation to analyze magnetic field properties in galaxy clusters, revealing a tangential magnetic field bias in cool-core clusters linked to internal gravity waves, contrasting with isotropic fields elsewhere.

Contribution

It is the first to connect tangential magnetic field orientations in cool-core clusters to internal gravity wave trapping, based on comprehensive simulation data.

Findings

Cool-core clusters exhibit tangential magnetic fields at ~0.1 r500c.

Magnetic fields are isotropic in non-cool-core clusters.

Tangential features can be transient or persistent over cosmic time.

Abstract

We characterize the magnetic field properties of 352 massive galaxy clusters from the TNG-Cluster magnetohydrodynamical cosmological simulation with a focus on central magnetic field morphology in cool-core (CC) vs 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 muG. We then discuss the main finding of this work: z=0 cool-core clusters have preferentially tangential magnetic fields at a characteristic scale of ~ 0.1 r500c. 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 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 cool-core TNG-Cluster halos, due to the strong entropy gradient in these clusters.