A non-ideal magnetohydrodynamic gadget: simulating massive galaxy clusters

Abstract

Magnetic fields in the intra‐cluster medium (ICM) of galaxy clusters have been studied in the past through different methods. So far, our understanding of the origin of these magnetic fields, as well as their role in the process of structure formation and their interplay with the other constituents of the ICM, is still limited. In the coming years, the up‐coming generation of radio telescopes is going to provide new data that will have the potential of setting constraints on the properties of magnetic fields in galaxy clusters. Here, we present zoomed‐in simulations for a set of massive galaxy clusters (Mv ≥ 1015 h−1 M⊙). This is an ideal sample to study the evolution of the magnetic field during the process of structure formation in detail. Turbulent motions of the gas within the ICM will manifest themselves in a macroscopic magnetic resistivity ηm, which has to be taken explicitly into account, especially at scales below the resolution limit. We have adapted the magnetohydrodynamic (MHD) gadget code by Dolag & Stasyszyn to include the treatment of the magnetic resistivity, and for the first time we have included non‐ideal MHD equations to better follow the evolution of the magnetic field within the galaxy clusters. We investigate which value of the magnetic resistivity ηm is required to match the magnetic field profile derived from radio observations. We find that a value of ηm∼ 6 × 1027 cm2 s−1 is necessary to recover the shape of the magnetic field profile inferred from radio observations of the Coma cluster. This value agrees well with the expected level of turbulent motions within the ICM at our resolution limit. The magnetic field profiles of the simulated clusters can be fitted by a β‐model‐like profile, with small dispersion of the parameters. We also find that the temperature, density and entropy profiles of the clusters depend on the magnetic resistivity constant, having flatter profiles in the inner regions when the magnetic resistivity increases.

Planckintermediate results

“…The turbulent re-acceleration model (Schlickeiser et al 1987;Brunetti et al 2001;Petrosian 2001) leads to a scaling of r ∝ n e T 1.5 ∝ y √ T in the B < B CMB limit (Cassano et al 2007) if one assumes B 2 ∝ n e which is close to the simulation scaling results of Bonafede et al (2011). Such a scaling relation is consistent with the observed correlation.…”

“…To remain consistent with the linear correlation found here, the magnetic field would thus need to be nearly independent of thermal density. The non-ideal MHD simulations of Bonafede et al (2011) show a typical scaling of B ∝ n 0.6 e , which would yield r ∝ y 2.2 /T 2.2 . This could make the secondary model inconsistent with the observations in the weak-field limit.…”

Ambipolar diffusion in smoothed particle magnetohydrodynamics

“…The simplest non-ideal MHD effect, Ohmic resistivity, has already been implemented into SPMHD by several authors (Bonafede et al 2011;Tsukamoto et al 2013), since it is a straightforward implementation of a diffusion term in SPH for which standard formulations exist (Brookshaw 1985;Cleary & Monaghan 1999). The other two non-ideal MHD effects, ambipolar diffusion and the Hall effect, are more complicated.…”

Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping

“…al in preparation) for a more detailed description, a first analysis of these set of simulations can be found in the recently submitted paper by Rasia et al (2015). The set of hydrodynamic simulations consists in re-simulations of 29 Lagrangian regions centered around the 29 most massive halos formed in a larger N-body cosmological simulation (see Bonafede et al 2011, for details on the initial conditions). The simulations, performed with the TreePM-SPH GADGET-3 code (Springel 2005), assume a flat ΛCDM cosmology with Ωm = 0.24, Ω b = 0.04, H0 = 72 km s −1 Mpc −1 , ns = 0.96 , σ8 = 0.8.…”