Merging Galaxy Clusters: Offset Between the Sunyaev-Zel'dovich Effect
  and X-ray Peaks
  Galaxy clusters, the most massive collapsed structures, have been routinely
used to determine cosmological parameters. When using clusters for cosmology,
the crucial assumption is that they are relaxed. However, subarcminute
resolution Sunyaev-Zel'dovich (SZ) effect images compared with high resolution
X-ray images of some clusters show significant offsets between the two peaks.
We have carried out self-consistent N-body/hydrodynamical simulations of
merging galaxy clusters using FLASH to study these offsets quantitatively. We
have found that significant displacements result between the SZ and X-ray peaks
for large relative velocities for all masses used in our simulations as long as
the impact parameters were about 100-250 kpc. Our results suggest that the SZ
peak coincides with the peak in the pressure times the line-of-sight
characteristic length and not the pressure maximum (as it would for clusters in
equilibrium). The peak in the X-ray emission, as expected, coincides with the
density maximum of the main cluster. As a consequence, the morphology of the SZ
signal and therefore the offset between the SZ and X-ray peaks change with
viewing angle. As an application, we compare the morphologies of our simulated
images to observed SZ and X-ray images and mass surface densities derived from
weak lensing observations of the merging galaxy cluster CL0152-1357. We find
that a large relative velocity of 4800 km/s is necessary to explain these
observations. We conclude that an analysis of the morphologies of
multi-frequency observations of merging clusters can be used to put meaningful
constraints on the initial parameters of the progenitors.
