Cold Fronts: Probes of Plasma Astrophysics in Galaxy Clusters
  The most massive baryonic component of galaxy clusters is the "intracluster
medium" (ICM), a diffuse, hot, weakly magnetized plasma that is most easily
observed in the X-ray band. Despite being observed for decades, the macroscopic
transport properties of the ICM are still not well-constrained. A path to
determine macroscopic ICM properties opened up with the discovery of "cold
fronts". These were observed as sharp discontinuities in surface brightness and
temperature in the ICM, with the property that the brighter (and denser) side
of the discontinuity is the colder one. The high spatial resolution of the
Chandra X-ray Observatory revealed two puzzles about the cold fronts. First,
they should be subject to Kelvin-Helmholtz instabilites, yet in many cases they
appear relatively smooth and undisturbed. Second, the width of the interface
between the two gas phases is typically narrower than the mean free path of the
particles in the plasma, indicating negligible thermal conduction. From the
time of their discovery, it was realized that these special characteristics of
cold fronts may be used to probe the physical properties of the cluster plasma.
In this review, we will discuss the recent simulations of cold front formation
and evolution in galaxy clusters, with a focus on those which have attempted to
use these features to constrain the physics of the ICM. In particular, we will
focus on the effects of magnetic fields, viscosity, and thermal conductivity on
the stability properties and long-term evolution of cold fronts. We conclude
with a discussion on what important questions remain unanswered, and the future
role of simulations and the next generation of X-ray observatories.
