On the X-Ray and Mass Distribution in the Merging Galaxy Cluster 1E   0657-56: Ram Pressure-Stripping in Substructures with an NFW Density Profile
  We investigate the X-ray and mass distribution in the merging galaxy cluster 1E 0657-56. We study head-on collisions of two virialized clusters with an NFW density profile in the $\Lambda$CDM universe using an N-body + hydrodynamical code. A clear off-set of an X-ray peak from a mass peak, which is like what is reported in Clow et al. (2004), is first reproduced in the N-body + hydrodynamical simulations. We estimate the ram pressure-stripping conditions of the substructure in mergers of two NFW dark halos using a simple analytical model. We find that the ram pressure dominates the gravity of the substructure when the smaller cluster's mass is less than approximately one tenth of the larger cluster's mass. The characteristic X-ray and mass structures found in 1E 0657-56 suggest that neither the ram pressure nor the gravitational bound force overwhelms the other and that the mass ratio between the progenitors is near the critical value mentioned above. 
Motokazu Takizawa (Yamagata University)