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 Hubble Space Telescope imaging data , we present a high resolution reconstruction of the mass distribution in the massive , lensing cluster Cl 0024+16 at z = 0.39 .
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 fiducial dark matter halo that hosts an early type L ^ { * } galaxy varies from M = 6.3 _ { -2.0 } ^ { +2.7 } \times 10 ^ { 11 } M _ { \odot } within r < 0.6 Mpc , 1.3 _ { -0.6 } ^ { +0.8 } \times 10 ^ { 12 } M _ { \odot } within r < 2.9 Mpc and increases further to M = 3.7 _ { -1.1 } ^ { +1.4 } \times 10 ^ { 12 } M _ { \odot } in the outskirts .
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 .
The mass of a dark matter subhalo that hosts a late-type L ^ { * } galaxy is 1.06 _ { -0.41 } ^ { +0.52 } \times 10 ^ { 12 } M _ { \odot } .
Early-type galaxies appear to be hosted on average in more massive dark matter subhalos compared to late-type galaxies .
Early-type galaxies also trace the overall mass distribution of the cluster whereas late-type galaxies are biased tracers .
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 observationally determined mass functions based on an I-band selected sample of cluster members and lensing data are in agreement with the shapes of the subhalo mass functions derived from the Millenium Run simulation .
However , simulated subhalos appear to be more efficiently stripped than lensing observations suggest .
This is likely an artifact of comparison with a dark matter only simulation .
Future simulations that simultaneously follow the detailed evolution of the baryonic component during cluster assembly will be needed for a more detailed comparison .