Cold Fronts by Merging of Shocks
  Cold fronts (CFs) are found in most galaxy clusters, as well as in some
galaxies and groups of galaxies. We propose that some CFs are relics of merging
between two shocks propagating in the same direction. Such shock mergers
typically result in a quasi-spherical, factor ~1.4-2.7 discontinuity in density
and in temperature. These CFs may be found as far out as the virial shock,
unlike what is expected in other CF formation models. As a demonstration of
this effect, we use one dimensional simulations of clusters and show that shock
induced cold fronts form when perturbations such as explosions or mergers occur
near the cluster's centre. Perturbations at a cluster's core induce periodic
merging between the virial shock and outgoing secondary shocks. These
collisions yield a distinctive, concentric, geometric sequence of CFs which
trace the expansion of the virial shock.
