  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)
