  Using adiabatic hydrodynamical simulations, we follow the evolution of two
symmetric cold fronts developing in the remnant of a violent z=0.3 massive
cluster merger. The structure and location of the simulated cold fronts are
very similar to those recently found in X-ray cluster observations, supporting
the merger hypothesis for the origin of at least some of the cold fronts. The
cold fronts are preceded by an almost spherical bow shock which originates at
the core and disappears after 1.6 Gyr. The cold fronts last longer and survive
until z=0. We trace back the gas mass constituting the fronts and find it
initially associated with the two dense cores of the merging clusters.
Conversely, we follow how the energy of the gas of the initial merging cores
evolves until z=0 from the merging and show that a fraction of this gas can
escape from the local potential well of the sub-clumps. This release occurs as
the sub-clumps reach their apocentre in an eccentric orbit and is due to
decoupling between the dark matter and part of the gas in the sub-clump because
of, first, heating of the gas at first close core passage and of, second, the
effect of the global cluster pressure which peaks as the centrifugal
acceleration of the sub-clump is maximal. The fraction of the gas of the
sub-clump liberated in the outbound direction then cools as it expands
adiabatically and constitutes the cold fronts.

Astrophysics