Astron. Astrophys. 348, 351-363 (1999)

SPH simulations of magnetic fields in galaxy clusters

K. Dolag ¹, M. Bartelmann ¹ and H. Lesch <sup>2

1</sup> Max-Planck-Institut für Astrophysik, P.O. Box 1523, D-85740 Garching, Germany
² Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany

Received 21 December 1998 / Accepted 16 June 1999

Abstract

We perform cosmological, hydrodynamic simulations of magnetic fields in galaxy clusters. The computational code combines the special-purpose hardware Grape for calculating gravitational interaction, and smooth-particle hydrodynamics for the gas component. We employ the usual MHD equations for the evolution of the magnetic field in an ideally conducting plasma. As a first application, we focus on the question what kind of initial magnetic fields yield final field configurations within clusters which are compatible with Faraday-rotation measurements. Our main results can be summarised as follows: (i) Initial magnetic field strengths are amplified by approximately three orders of magnitude in cluster cores, one order of magnitude above the expectation from spherical collapse. (ii) Vastly different initial field configurations (homogeneous or chaotic) yield results that cannot significantly be distinguished. (iii) Micro-Gauss fields and Faraday-rotation observations are well reproduced in our simulations starting from initial magnetic fields of strength at redshift 15. Our results show that (i) shear flows in clusters are crucial for amplifying magnetic fields beyond simple compression, (ii) final field configurations in clusters are dominated by the cluster collapse rather than by the initial configuration, and (iii) initial magnetic fields of order are required to match Faraday-rotation observations in real clusters.

Key words: magnetic fields galaxies: clusters: general cosmology: theory

Send offprint requests to: Klaus Dolag

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Contents

• 1. Introduction
• 2. GrapeSPH combined with MHD
  • 2.1. GRAPE
  • 2.2. SPH
  • 2.3. MHD
• 3. Initial conditions
  • 3.1. Cosmology
  • 3.2. Primordial magnetic fields
  • 3.3. Simulation parameters
• 4. Tests of the code
  • 4.1. Co-planar MHD Riemann problem
  • 4.2. Divergence of B
• 5. Qualitative results
  • 5.1. Importance of shear flows
  • 5.2. Field structure
  • 5.3. Radio and Inverse-Compton emission
  • 5.4. Faraday rotation
• 6. Statistics of Faraday rotation measures
  • 6.1. Different initial field set-ups
  • 6.2. Varying initial field strengths
• 7. Comparison with observed data
  • 7.1. Individual clusters
  • 7.2. A sample of clusters
• 8. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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