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 $z=0.17$ to 0.58, utilizing high-quality archival {\it Hubble Space Telescope} ({\it HST}) 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 $L^{\ast }$ cluster members in a statistical fashion. The fraction of total mass associated with individual galaxies within the inner regions of these clusters ranges from 10–20% 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 ($>3$-$\sigma$ significance) that a fiducial early-type $L^{\ast }$ galaxy in these clusters has a mass distribution that is tidally truncated compared to equivalent luminosity galaxies in the field. In fact, we exclude field galaxy scale dark halos for these cluster early-types at $>10$-$\sigma$ significance. We compare the tidal radii obtained from this lensing analysis with the central density of the cluster potentials and find a correlation which is in excellent agreement with theoretical expectations of tidal truncation: $\log [r_t*] \propto (-0.6\pm 0.2) \log [\rho_0]$.