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Christoph Pfrommer

Currently, I am leading the research group Cosmology and High-energy Astrophysics at the Leibniz-Institute for Astrophysics Potsdam (AIP) and doing research as a jointly appointed professor at the University of Potsdam.

Part of the new research group is funded by the European Research Council through a Consolidator Grant for my project CRAGSMAN, which seeks to understand The Impact of Cosmic Rays on Galaxy and Cluster Formation. At the same time, we are continuing our work on understanding the emergence of large-scale structure in the Local Universe as well as pursuing exciting research on topics in high-energy astrophysics.

Research interests
  • Cosmology. Formation and evolution of galaxies, galaxy clusters, and large-scale structure in the Universe; intergalactic medium and Lyman-α forest; supermassive black holes; cosmological parameter estimation from cluster surveys.

  • High-Energy Astrophysics. Cosmic rays, magnetic fields, and radiative processes in galaxies and galaxy clusters; propagation of ultra-relativistic gamma rays from blazars, pair creation and plasma instabilities; dark matter theory and indirect detection methods.

  • Computational Astrophysics. High-performance computing with the smoothed particle hydrodynamics code GADGET, the adaptive mesh refinement code FLASH, and the unstructured moving mesh code AREPO.

  • Radio- and Gamma-Ray Astronomy. Associate member of the LOFAR Magnetism Key Science Project; external collaboration member of the Cherenkov telescopes MAGIC, VERITAS, and the Fermi Space Telescope Collaboration.

Magnetic Field in the Virgo Cluster
Current Research download PDF
Detection of magnetic field orientations in galaxy clusters

Clusters of galaxies, filled with hot, magnetised plasma, are the largest bound objects in existence and an important touchstone in understanding the formation of structures in our Universe. Magnetic fields strongly shape the clusters' thermal histories, which remain mysterious; some cores should have long since cooled and collapsed. In a seemingly unrelated puzzle, recent observations of Virgo cluster spiral galaxies imply ridges of strong, coherent magnetic fields offset from their centre. Here we demonstrate, using 3D magneto-hydrodynamical simulations, that such ridges are easily explained by galaxies sweeping up field lines as they orbit inside the cluster. This magnetic drape is then literally lit up with cosmic rays from the galaxies' stars, generating coherent polarised emission at the galaxies' leading edges. This immediately presents a first technique for probing local orientations and characteristic length scales of cluster magnetic fields. The first application of this technique, mapping the field of the Virgo cluster, gives a startling result - the magnetic field is preferentially oriented radially, suggesting a mechanism for maintaining some clusters in a 'non-cooling-core' state.

Signature figures:

Signature movies:

The first three panels show a Quicktime movie of the simulated polarised synchrotron radiation viewed from various angles and with two field orientations as studied in this work by Pfrommer & Dursi, 2010, Nature Phys. 6, 520-526, arXiv:0911.2476. The movie is also available in windows media.

The last panel shows a Quicktime movie of a 3d rendering of the draping process on a spherical object as studied in Dursi & Pfrommer, 2008, ApJ, 677, 993, arXiv:0711.0213. The movie is also available in mpeg or windows media. More information about magnetic draping in clusters is available at this http URL.