The Distribution of Dark Matter Over 3 Decades in Radius in the Lensing Cluster Abell 611

TL;DR

This study combines multiple observational techniques to map the dark matter distribution in galaxy cluster Abell 611 over a large radius, revealing deviations from standard models and suggesting new insights into baryon-dark matter interactions.

Contribution

It introduces an integrated methodology combining weak lensing, strong lensing, and stellar kinematics to accurately profile dark matter in galaxy clusters over a wide range of scales.

Findings

Dark matter profile extends from ~3 kpc to 3.25 Mpc.

NFW profile does not fit the observed data.

Inner dark matter slope is flatter than 0.3.

Abstract

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.