Magnetic fields in clusters Marcus Brüggen Elke Rödiger, Huub Röttgering, Reinout van Weeren, Mateusz Ruszkowski, Evan Scannapieco,Torsten Ensslin, Sebastian Heinz, Mitch Begelman, Matthias.

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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. 2006
1061 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
lB  dbub
lB  dbub
Ruszkowski, Ensslin, Brüggen, Heinz & Pfrommer (2007)
tCoul ~ 2.5 10  n yr
8
1
2 2
tBIC ~ 2.3 10  (1  uB / uIC ) yr
8
1
4
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
Could it be turbulence?
Scannapieco & MB
(ApJ in press)
astro-ph 0806.3268
No Turbulence
No Shocks
Turb+Shocks
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

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