A wide-field spectroscopic survey of the cluster of galaxies Cl0024+1654 - II. A high-speed collision?

The mass distribution of the rich cluster of galaxies C10024+1654 has frequently been used to constrain the nature of dark matter, yet a model consistent with all the observational data has been difficult to construct. In this paper we analyse the three-dimensional structure of this cluster using new spectroscopic information on similar to300 galaxies within a projected radius of 3 h(-1) Mpc. These data reveal an unusual foreground component of galaxies separated from the main cluster by 3000 km s(-1). We use numerical simulations to show that a high speed collision along the line of sight between C10024+1654 and a second cluster of slightly smaller mass can reproduce the observed peculiar redshift distribution. Such a collision would dramatically alter the internal mass distribution of the bound remnants, creating constant density cores from initially cuspy dark matter profiles and scattering galaxies to large projected radii, consistent with the observed distribution of galaxies in C10024+1654. The proposed scenario can reconcile the inferred mass profile from gravitational lensing with predictions from hierarchical structure formation models, while at the same time resolving the mass discrepancy that results from a comparison between lensing, velocity dispersion and X-ray studies.