Evidence for Tidal Stripping of Dark Matter Halos in Massive Cluster Lenses

In this Letter, we present the results of our study of galaxy-galaxy lensing in massive cluster lenses spanning z=0.17-0.58, utilizing high-quality archival Hubble Space Telescope data. Local anisotropies in the shear maps are assumed to arise from dark matter substructure within these clusters. Associating the substructure with bright early-type cluster galaxies, we quantify the properties of typical L^* cluster members in a statistical fashion. The fraction of total mass associated with individual galaxies within the inner regions of these clusters ranges from 10% to 20%, implying that the bulk of the dark matter in massive lensing clusters is smoothly distributed. Looking at the properties of the cluster galaxies, we find strong evidence (>3 σ significance) that a fiducial early-type L^* galaxy in these clusters has a mass distribution that is tidally truncated compared with equivalent luminosity galaxies in the field. In fact, we exclude field galaxy scale dark halos for these cluster early types at greater than 10 σ significance. We compare the tidal radii obtained from this lensing analysis with the central density of the cluster potentials and find a correlation that is in excellent agreement with theoretical expectations of tidal truncation: logr^*_t~(-0.6+/-0.2)logρ₀.