Christoph's photo Christoph Pfrommer Welcome to the home page of

Christoph Pfrommer

Currently, I'm holding a senior research associate position in theoretical astrophysics at the Heidelberg Institute for Theoretical Studies (HITS) where I work with Volker Springel.


Research interests

  • High-Energy Astrophysics. Cosmic-ray acceleration, transport, and hadronic interactions; non-thermal radiative emission: synchrotron, inverse Compton, and pion-decay; interaction of magnetized plasma with galaxies, galaxy groups, and radio bubbles; dark matter annihilation and decay; propagation of ultra-relativistic gamma-rays, pair-creation and plasma instabilities; extragalactic gamma-ray background.

  • Cosmology. Cosmological hydrodynamical simulations of the formation of galaxies, galaxy clusters, large-scale structure, and the Lyman-α forest; secondary anisotropies of the CMB, including the Sunyaev-Zel'dovich effect; cosmological parameter estimation from cluster surveys; gravitational weak lensing.

  • Computational Astrophysics. High-performance computing using the cosmological SPH code GADGET and the general purpose AMR hydrodynamics code FLASH; simulations including cosmic ray transport and magneto-hydrodynamics (MHD).

  • Radio- and Gamma-Ray Astrophysics. Associate member of LOFAR, Magnetism Key Science Project; external collaboration member of the imaging atmospheric 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.


Recent talk about Non-thermal emission from galaxy clusters,  download PDF