INTRODUCTION

We use the cosmological MHD code described in Dolag et al. (1999) and Dolag et al. (2002) to simulate the formation of magnetised galaxy clusters from an initial density perturbation field. The code combines the merely gravitational interaction of a dark-matter component with the hydrodynamics of a gaseous component. It was also supplemented with the magneto-hydrodynamic equations to trace the evolution of the magnetic fields which are frozen into the motion of the gas because of its assumed ideal electric conductivity. The code also assumes the intra-cluster medium to be an ideal gas with an adiabatic index of 5/3 and without cooling.

See Research Highlights: Magnetic Fields in Galaxy Clusters An Obscure Ingredient of Galaxy Clusters

Our simulations work with three classes of particles. In a central region, we have about 50,000 collision-less dark-matter particles, mixed with an equal number of gas particles. The colour of the displayed gas particles is chosen according to their density. The colours range form blue for low density over green and yellow to red for high density. These gas particles carry the magnetic field. The central region is surrounded by about 20,000 collision-less boundary particles whose mass increases outward to mimic the tidal forces of the neighbouring large scale structure. The figure shows the structure of this kind of simulation at redshift z=0 from the whole simulated volume down to the cluster. The lower box in this figure shows one simulated cluster in a three-dimensional box and also appears in colour. The Faraday-rotation measures produced by the cluster in the three independent spatial directions are projected onto the box sides and encoded by colour as indicated below the box. The gray solid curves are projected density contours, whereas the dashed line marks half the central density. The green dashed curve encompasses the projected region emitting 90% of the X-ray luminosity. The shaded object in the centre is the isodensity surface at hundred times the critical density. In addition, magnetic field vectors are plotted in the slice marked by the purple rectangle. Coordinates are physical coordinates in Mpc.

SCDM (=0.5, =1.0, =0.0, =1.2)

LCDM (=0.7, =0.3, =0.7, =1.05)

So far, we have a set of ten realisations for two different cosmologies. The figure shows the comparison of simulated results with a sample of measurements in Abell clusters. The absolute values of Faraday rotation measurements (Kim et al. 1991) vs. radius in units of the Abell radius are shown as points. Obviously, the dispersion increases towards the cluster centre. The solid curves mark the median (red) and the 25- and 75-percentiles (black) of the measurements. The blue lines are the medians obtained from simulated cluster samples starting with a low (dotted), medium (dashed) and high (dash-dotted) initial magnetic field.

So far, we have a set of ten realisations for two different cosmologies. Each of these clusters have been simulated starting with different initial magnetic field strengths and orientations. This leads to more than 100 simulated, magnetized galaxy clusters. If you are interested in working with these cluster catalog, please contact Klaus Dolag.

SCDM	LCDM		Data Access Data and I/O example to read the Data can be found here.
Homogeneous Initial Field
No	No
Low	Low
Medium	Medium
High	High
Chaotic Initial Field
Low

Here you can down-load a very reduced version of a movie, showing how a magnetised cluster forms. It contains 4 parts, showing
• The simulation as it is evolved at redshift 3. The simulation volume is rotated to show the 3D filamentary structure.
  
• The simulation evolving towards today. The black dots denote the dark matter particle, colored dots are the gas particles.
  
• The central part where the cluster forms in the simulation is now shown, again for the evolution between redshift 3 and today. Shown are the X-ray emission and the temperature. Note the shocks running through the cluster during merger events.
  
• Now a bigger volume around the cluster center is shown for the same time sequent. This time the visualisation focus on quantities related to the magnetic field. Watch how the Faraday rotation measure maps change during a merger event.
  
Movie ( MOV, 8.1Mb)


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SUGGESTED READING:
• Klaus Dolag, Matthias Bartelmann and Harald Lesch,
  SPH simulations of magnetic fields in galaxy clusters
  Astronomy & Astrophysics, 348, 351

• Dolag and Enßlin
  Radio Halos of Galaxy Clusters from Hadronic Secondary Electron Injection in Realistic Magnetic Field Configurations
  Astronomy & Astrophysics, 362, 151

• Dolag and Schindler
  The effect of magnetic fields on the mass determination of clusters of galaxies
  Astronomy & Astrophysics, 364, 491

• Dolag, Evrard and Bartelmann,
  The temperature-mass relation in magnetized galaxy clusters
  Astronomy & Astrophysics, 369, 36

• Dolag, Schindler, Govoni & Feretti
  Correlation of the magnetic field and the intra-cluster gas density in galaxy clusters
  Astronomy & Astrophysics, 378, 777

• Dolag, Bartelmann & Lesch
  Evolution and structure of magnetic fields in simulated galaxy clusters
  accepted by A&A

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Go to NumCos at MPA

Comments to: Klaus Dolag ( kdolag@mpa-garching.mpg.de)