A Wide-Field Hubble Space Telescope Study of the Cluster Cl 0024+1654 at z=0.4. II. The Cluster Mass Distribution

We present a comprehensive lensing analysis of the rich cluster Cl 0024+1654 (z=0.395) based on panoramic sparse-sampled imaging conducted with the WFPC2 and STIS cameras on board the Hubble Space Telescope. By comparing higher fidelity signals in the limited STIS data with the wider field data available from WFPC2, we demonstrate an ability to detect reliably weak-lensing signals to a cluster radius of ~=5 h^-1₆₅ Mpc, where the mean shear is around 1%. This enables us to study the distribution of dark matter with respect to the cluster light over an unprecedented range of cluster radii and environments. The projected mass distribution reveals a secondary concentration representing 30% of the overall cluster mass, which is also visible in the distribution of cluster member galaxies. We develop a method to derive the projected mass profile of the main cluster taking into account the influence of the secondary clump. We normalize the mass profile determined from the shear by assuming that background galaxies selected with 23<I<26 have a redshift distribution statistically similar to that inferred photometrically in the Hubble Deep Fields. The total mass within the central region of the cluster is independently determined from strong-lensing constraints according to a detailed model that utilizes the multiply imaged arc at z=1.675. Combining strong and weak constraints, we are able to probe the mass profile of the cluster on scales of 0.1-5 Mpc, thus providing a valuable test of the universal form proposed by Navarro, Frenk, & White (NFW) on large scales. A generalized power-law fit indicates an asymptotic three-dimensional density distribution of ρ~r^-n with n>2.4. An isothermal mass profile is therefore strongly rejected, whereas an NFW profile with M₂₀₀=6.1^+1.2_-1.1×10¹⁴ h^-1₆₅ M_solar provides a good fit to the lensing data. We isolate cluster members according to their optical/near-infrared colors; the red cluster light closely traces the dark matter with a mean mass-to-light ratio of M/L_K=40+/-5 h₆₅ M_solar/L_solar. Similar profiles for mass and light on 1-5 Mpc scales are expected if cluster assembly is largely governed by infalling groups.