Evolution and structure of magnetic fields in simulated galaxy clusters

Abstract

Abstract. We use cosmological magneto-hydrodynamic simulations to study the evolution of magnetic fields in galaxy clusters in two different cosmological models, a standard-CDM and a Λ-CDM model. We show that the magnetic field strength profiles closely follow the cluster density profiles outside a core region of radius ∼200 h −1 kpc. The magnetic field has a correlation length of order 50 h −1 kpc and reverses on scales of ∼100 h −1 kpc along typical lines-of-sight. The power spectrum of the magnetic field can well be approximated by a steep power law with an exponent of ∼−2.7. The mean magnetic field in the cluster cores grows roughly exponentially with decreasing redshift, B ∼ 10 −2.5z µG. Merger events have a pronounced effect on magnetic field evolution, which is strongly reflected in measurable quantities like the Faraday rotation. The field evolution in the two different cosmologies proceeds virtually identically. All our cluster models very well reproduce observed Faraday rotation measurements when starting with nG seed fields.

Extragalactic propagation of ultrahigh energy cosmic-rays

“…More recently, the discussion of the effect of the EGMF enhancement in large scale structures has been undertaken using large structure formation simulations including MHD treatment for the evolution of the magnetic fields [144,145,146,147,148,150,151] (some of these simulations being constrained by the local density velocity field to provide more realistic field configurations in the local universe). These simulations rely on different assumptions on the origin of the fields and the mechanisms involved in their growth.…”

Simulations of Merging Clusters of Galaxies

“…For these hydrodynamic calculations two different methods have mainly been used: (1) Smoothed Particle Hydrodynamics (Lagrangian approach, e.g. Evrard 1990;Dolag et al 1999;Takizawa 1999;Takizawa &;Naito 2000) in which the gas is treated as particles and (2) grid codes (Eulerian approach, e.g. Schindler & Miiller 1993;Bryan et al 1994;Roettiger et al 1996Roettiger et al , 1997Roettiger et al , 1998Roettiger et al , 1999aRicker 1998;Quilis et al 1998) …”

“…the gas density is increased, and as the X-ray emission is proportional to the square of the density we see enhanced X-ray emission during the passage. During the core passage and at each rebounce an increase in the magnetic field is visible (Dolag et al 1999(Dolag et al , 2000; Roettiger et al 1999b; see also Section 6). Mergers also cause a lot of turbulence.…”

“…Therefore magnetohydrodynamic calculations have been performed (Dolag et al 1999;Roettiger et al 1999b). It has been found that the initial field distribution is irrelevant for the final structure of the magnetic field.…”

Magnetic fields and Turbulence in Star Formation using Smoothed Particle Hydrodynamics

“…Around the same time Meglicki (1995) applied a non-conservative SPMHD formulation to magnetic fields in the Galaxy. The period after these works saw a few but limited applications of SPMHD to 'real' astrophysical problems, including notably an application to magnetic fields in galaxy clusters by Dolag, Bartelmann & Lesch (1999) † and at least one foray into star formation by Byleveld & Pongracic (1996). However it would be fair to say that there was no real consensus on a standard approach and that many problems remained.…”