Unopposed radiative cooling in clusters of galaxies results in excessive mass
deposition rates. However, the cool cores of galaxy clusters are continuously
heated by thermal conduction and turbulent heat diffusion due to minor mergers
or the galaxies orbiting the cluster center. These processes can either reduce
the energy requirements for AGN heating of cool cores, or they can prevent
overcooling altogether. We perform 3D MHD simulations including field-aligned
thermal conduction and self-gravitating particles to model this in detail.
Turbulence is not confined to the wakes of galaxies but is instead
volume-filling, due to the excitation of large-scale g-modes. We systematically
probe the parameter space of galaxy masses and numbers. For a wide range of
observationally motivated galaxy parameters, the magnetic field is randomized
by stirring motions, restoring the conductive heat flow to the core. The
cooling catastrophe either does not occur or it is sufficiently delayed to
allow the cluster to experience a major merger that could reset conditions in
the intracluster medium. Whilst dissipation of turbulent motions is negligible
as a heat source, turbulent heat diffusion is extremely important; it
predominates in the cluster center. However, thermal conduction becomes
important at larger radii, and simulations without thermal conduction suffer a
cooling catastrophe. Conduction is important both as a heat source and to
reduce stabilizing buoyancy forces, enabling more efficient diffusion.
Turbulence enables conduction, and conduction enables turbulence. In these
simulations, the gas vorticity---which is a good indicator of trapped
g-modes--increases with time. The vorticity growth is approximately mirrored by
the growth of the magnetic field, which is amplified by turbulence.Comment: Submitted to MNRA
