The Distribution of Dark Matter Over 3 Decades in Radius in the Lensing
  Cluster Abell 611
  We present a detailed analysis of the baryonic and dark matter distribution
in the lensing cluster Abell 611 (z=0.288), with the goal of determining the
dark matter profile over an unprecedented range of cluster-centric distance. By
combining three complementary probes of the mass distribution, weak lensing
from deep multi-color imaging, strong lensing constraints based on the
identification of multiply-imaged sources, and resolved stellar velocity
dispersion measures for the brightest cluster galaxy (BCG), we extend the
methodology for separating the dark and baryonic mass components introduced by
Sand et al. (2008). Our resulting dark matter profile samples the cluster from
~3 kpc to 3.25 Mpc, thereby providing an excellent basis for comparisons with
recent numerical models. We demonstrate that only by combining our three
observational techniques can degeneracies in constraining the form of the dark
matter profile be broken on scales crucial for detailed comparisons with
numerical simulations. Our analysis reveals that a simple Navarro, Frenk, and
White (NFW) profile is an unacceptable fit to our data. We confirm earlier
claims that the inner profile of the dark matter profile deviates significantly
from the NFW form and find a inner logarithmic slope \beta flatter than 0.3
(68%; where rho_DM ~ r^{-\beta} at small radii). In order to reconcile our data
with cluster formation in a LambdaCDM cosmology, we speculate that it may be
necessary to revise our understanding of the nature of baryon--dark matter
interactions in cluster cores. Comprehensive weak and strong lensing data, when
coupled with kinematic information on the brightest cluster galaxy, can readily
be applied to a larger sample of clusters to test the universality of these
results.
