Measuring the Mass Distribution in Galaxy Clusters
  Cluster mass profiles are tests of models of structure formation. Only two
current observational methods of determining the mass profile, gravitational
lensing and the caustic technique, are independent of the assumption of
dynamical equilibrium. Both techniques enable determination of the extended
mass profile at radii beyond the virial radius. For 19 clusters, we compare the
mass profile based on the caustic technique with weak lensing measurements
taken from the literature. This comparison offers a test of systematic issues
in both techniques. Around the virial radius, the two methods of mass
estimation agree to within about 30%, consistent with the expected errors in
the individual techniques. At small radii, the caustic technique overestimates
the mass as expected from numerical simulations. The ratio between the lensing
profile and the caustic mass profile at these radii suggests that the weak
lensing profiles are a good representation of the true mass profile. At radii
larger than the virial radius, the lensing mass profile exceeds the caustic
mass profile possibly as a result of contamination of the lensing profile by
large-scale structures within the lensing kernel. We highlight the case of the
closely neighboring clusters MS0906+11 and A750 to illustrate the potential
seriousness of contamination of the the weak lensing signal by unrelated
structures.
