The survival of dark matter halos in the cluster Cl0024+16

Theories of structure formation in a cold dark matter dominated Universe predict that massive clusters of galaxies assemble from the hierarchical merging of lower mass subhalos. Exploiting strong and weak gravitational lensing signals inferred from panoramic HST imaging data, we present a high resolution reconstruction of the mass distribution in the massive, lensing cluster Cl0024+16. Applying galaxy-galaxy lensing techniques we track the fate of dark matter subhalos as a function of projected cluster-centric radius out to 5 Mpc, well beyond the virial radius. We report the first detection of the statistical lensing signal of dark matter subhalos associated with late-type galaxies in clusters. The mass of a typical dark matter subhalo that hosts an L* galaxy increases with projected cluster-centric radius in line with expectations from the tidal stripping hypothesis. Early-type galaxies appear to be hosted on average in more massive dark matter subhalos compared to late-type galaxies. We interpret our findings as evidence for the active assembly of mass via tidal stripping in galaxy clusters. The mass function of dark matter subhalos as a function of projected cluster-centric radius, is compared with an equivalent mass function derived from clusters in the Millenium Run simulation populated with galaxies using semi-analytic models. The shape of the lensing determined mass functions are in very good agreement with the subhalo mass functions derived from the Millenium Run simulation. However, simulated subhalos appear to be more efficiently stripped than lensing observations suggest. (Abridged)