"The Cluster(s) of Galaxies Cl0024+1654" 

Oliver Czoske
Institute for Astronomy
Observatoire Midi-Pyrenees, Toulouse, France


I present a wide-field spectroscopic survey of the well-known lensing
cluster Cl0024+1654 at z=0.395, covering 4 x 4.8 (Mpc/h)^2 at the
cluster redshift. The catalogue includes 650 redshifts of which about
300 are in the neighbourhood of the mean cluster redshift. The
redshift distribution turns out to be distinctly bimodal with a
separation of the two modes of  dz = 0.007 or 3000 km/s. I develop a
possible scenario for this redshift distribution which assumes that we
are actually seeing two clusters just emerging from a near-radial
high-speed collision. This scenario can explain several of the
mysteries surrounding Cl0024, namely the flat (and CDM-unlike) central
mass distribution as derived from strong lensing modelling and the 
discrepancy between mass estimates from different methods.