Magnetic fields in clusters Marcus Brüggen Elke Rödiger, Huub Röttgering, Reinout van Weeren, Mateusz Ruszkowski, Evan Scannapieco,Torsten Ensslin, Sebastian Heinz, Mitch Begelman, Matthias Hoeft, Paola Rebusco, Hans Böhringer, Eugene Churazov, Aurora Simionescu

Questions: 1. What produces large-scale magnetic fields in clusters and filaments? 2. What role do magnetic fields play in clusters?

Possible answers: 1.Amplification of primordial seed fields by gravitational collapse of structures Q: How big does the seed field have to be if this is the dominant mechanism? Q: Where does seed field come from? Pop III stars? First AGN? Shocks? Batteries?

2.Injection of magnetic fields by stars and AGN etc. Q: How do magnetic fields diffuse out into IGM? Hydra A X-ray (blue) + Radio (330 MHz, 1.4 GHz) Wise et al erg

Emission line filaments in NGC1275 in centre of Perseus cluster Fabian et al. Nature 2008 HST

Another problem: Shape of bubbles... Diehl et al. 2008

Ruszkowski, Ensslin, Brüggen, Heinz & Pfrommer (2007)

Simulations of bubbles with magnetic fields and anisotropic diffusion of cosmic rays substantial fraction of CR remains confined to bubble even if parallel diffusivity is high isotropic diffusion is ruled out by radio observations partial escape of CR is confined to wake of bubble escaping CR could account for excitation of H alpha filaments trailing behind bubbles in Perseus cluster CR could produce gamma-rays upon interaction with ICM

No TurbulenceNo Shocks Turb+Shocks Scannapieco & MB (ApJ in press) astro-ph Could it be turbulence?

What we learned from our MareNostrum simulations shock detection in postprocessing in a cosmological simulation works several clusters in MareNostrum Universe show relic-like features maximum diffuse radio emission depends strongly on X-ray temperature Accretion shocks produce only very little radio emission moderate efficiency of shock acceleration (0.005) and magnetic fields (sub-microG) fields suffice to reproduce number density and luminosity of radio relics AMR simulations under way

Radio filaments (WHIM in radio?) 29 candidates spectral index < -1.7 diffuse > 20 arcsec not associated with group or clusters Röttgering, van Weeren, MB

Take home messages : Magnetic fields are important for bubble morphology and cosmic ray transport we can predict statistical properties of diffuse radio emission from cosmological simulations deep surveys of relics constrains magnetic fields in periphery of clusters LOFAR observations of X-ray cavities allows you to to determine content of radio lobes and ICM magnetic field we might be able to detect the WHIM in the radio