Dynamical evolution of magnetic fields in the intracluster medium
  We investigate the evolution of magnetic fields in galaxy clusters starting
from constant primordial fields using highly resolved ($\approx \rm 4 ~kpc$)
cosmological MHD simulations. The magnetic fields in our sample exhibit
amplification via a small-scale dynamo and compression during structure
formation. In particular, we study how the spectral properties of magnetic
fields are affected by mergers, and we relate the measured magnetic energy
spectra to the dynamical evolution of the intracluster medium. The magnetic
energy grows by a factor of $\sim$ 40-50 in a time-span of $\sim 9$ Gyr and
equipartition between kinetic and magnetic energy occurs on a range of scales
($< 160 \rm ~kpc$ at all epochs) depending on the turbulence state of the
system. We also find that, in general, the outer scale of the magnetic field
and the MHD scale are not simply correlated in time. The effect of major
mergers is to shift the peak magnetic spectra to it smaller scales, whereas the
magnetic amplification only starts after $\lesssim$ 1 Gyr. In contrast,
continuous minor mergers promote the steady growth of the magnetic field. We
discuss the implications of these findings in the interpretation of future
radio observations of galaxy clusters.
