Zusammenfassung
The existence of microgauss magnetic fields in galaxy clusters have been
established through observations of synchrotron radiation and Faraday rotation.
They are conjectured to be generated via small-scale dynamo by turbulent flow
motions in the intracluster medium (ICM). Some of giant radio relics, on the
other hand, show structures of synchrotron polarization vectors, organized over
the scales of $\sim$ Mpc, challenging the turbulence origin of cluster magnetic
fields. Unlike turbulence in the interstellar medium, turbulence in the ICM is
subsonic. And it is driven sporadically in highly stratified backgrounds, when
major mergers occur during the hierarchical formation of clusters. To
investigate quantitatively the characteristics of turbulence dynamo in such ICM
environment, we have performed a set of turbulence simulations using a
high-order-accurate, magnetohydrodynamic (MHD) code. We find that turbulence
dynamo could generate the cluster magnetic fields up to the observed levels
from primordial seed fields of $10^-15$ G or so within the age of the
universe, if the MHD description of the ICM could be extended down to $\sim$
kpc scales. However, highly organized structures of polarization vectors such
as those observed in the Sausage relic are difficult to be reproduced by the
shock compression of turbulence-generated magnetic fields. This implies that
the modeling of giant radio relics may require fossil magnetic field structures
left from extinct radio jets.
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