First results from the IllustrisTNG simulations: radio haloes and magnetic fields

TL;DR

The paper presents initial findings from the IllustrisTNG simulations, demonstrating how magnetic fields and radio haloes in galaxy clusters develop and compare with observations, highlighting the link between structure formation and magnetic phenomena.

Contribution

This study introduces the IllustrisTNG simulation suite and models magnetic fields and radio emission in galaxy clusters, providing new insights into their properties and observational signatures.

Findings

Magnetic fields are amplified from seed fields to observed strengths in low-redshift galaxies.

Simulated radio emission correlates with cluster mass and matches observed scaling relations.

Surface brightness profiles of simulated clusters agree with VLA observations of Coma and Perseus.

Abstract

We introduce the IllustrisTNG project, a new suite of cosmological magnetohydrodynamical simulations performed with the moving-mesh code AREPO employing an updated Illustris galaxy formation model. Here we focus on the general properties of magnetic fields and the diffuse radio emission in galaxy clusters. Magnetic fields are prevalent in galaxies, and their build-up is closely linked to structure formation. We find that structure formation amplifies the initial seed fields ($10^{-14}$ comoving Gauss) to the values observed in low-redshift galaxies ($1-10\,\mu{\rm G}$). The magnetic field topology is closely connected to galaxy morphology such that irregular fields are hosted by early-type galaxies, while large-scale, ordered fields are present in disc galaxies. Using two simple models for the energy distribution of relativistic electrons we predict the diffuse radio emission of $280$ clusters with a baryonic mass resolution of $1.1\times 10^{7}\,{\rm M_{\odot}}$, and generate mock observations for VLA, LOFAR, ASKAP and SKA. Our simulated clusters show extended radio emission, whose detectability correlates with their virial mass. We reproduce the observed scaling relations between total radio power and X-ray emission, $M_{500}$, and the Sunyaev-Zel'dovich $Y_{\rm 500}$ parameter. The radio emission surface brightness profiles of our most massive clusters are in reasonable agreement with VLA measurements of Coma and Perseus. Finally, we discuss the fraction of detected extended radio haloes as a function of virial mass and source count functions for different instruments. Overall our results agree encouragingly well with observations, but a refined analysis requires a more sophisticated treatment of relativistic particles in large-scale galaxy formation simulations.