Turbulent Pressure Support in the Outer Parts of Galaxy Clusters
  We use three-dimensional MHD simulations with anisotropic thermal conduction
to study turbulence due to the magnetothermal instability (MTI) in the
intracluster medium (ICM) of galaxy clusters. The MTI grows on timescales of ~1
Gyr and is capable of driving vigorous, sustained turbulence in the outer parts
of galaxy clusters if the temperature gradient is maintained in spite of the
rapid thermal conduction. If this is the case, turbulence due to the MTI can
provide up to 5-30% of the pressure support beyond r_500 in galaxy clusters, an
effect that is strongest for hot, massive clusters. The turbulence driven by
the MTI is generally additive to other sources of turbulence in the ICM, such
as that produced by structure formation. This new source of non-thermal
pressure support reduces the observed Sunyaev-Zel'dovich (SZ) signal and X-ray
pressure gradient for a given cluster mass and introduces a cluster mass and
temperature gradient-dependent bias in SZ and X-ray mass estimates of clusters.
This additional physics may also need to be taken into account when estimating
the matter power spectrum normalization, sigma-8, through simulation templates
from the observed amplitude of the SZ power spectrum.
