  The average mass density profile measured in the CNOC cluster survey is well
described with the analytic form rho(r)=A/[r(r+a_rho)^2], as advocated on the
basis on n-body simulations by Navarro, Frenk & White. The predicted core radii
are a_rho=0.20 (in units of the radius where the mean interior density is 200
times the critical density) for an Omega=0.2 open CDM model, or a_rho=0.26 for
a flat Omega=0.2 model, with little dependence on other cosmological parameters
for simulations normalized to the observed cluster abundance. The dynamically
derived local mass-to-light ratio, which has little radial variation, converts
the observed light profile to a mass profile. We find that the scale radius of
the mass distribution, 0.20<= a_rho <= 0.30 (depending on modeling details,
with a 95% confidence range of 0.12-0.50), is completely consistent with the
predicted values. Moreover, the profiles and total masses of the clusters as
individuals can be acceptably predicted from the cluster RMS line-of-sight
velocity dispersion alone. This is strong support of the hierarchical
clustering theory for the formation of galaxy clusters in a cool,
collisionless, dark matter dominated universe.
