The Dark Matter Distribution in Abell 383: Evidence for a Shallow Density Cusp from Improved Lensing, Stellar Kinematic and X-ray Data

TL;DR

This study combines multiple observational techniques to analyze the dark matter distribution in Abell 383, providing strong evidence for a shallow density cusp and challenging current high-resolution simulation predictions.

Contribution

It presents the most robust measurement of a shallow dark matter density slope in a galaxy cluster using combined lensing, stellar kinematics, and X-ray data with advanced modeling.

Findings

Dark matter density slope .0 (95% confidence) at small radii.

First stellar velocity dispersion profile measured to 26 kpc in a lensing cluster.

Triaxial and axisymmetric models improve the robustness of the analysis.

Abstract

We extend our analyses of the dark matter (DM) distribution in relaxed clusters to the case of Abell 383, a luminous X-ray cluster at z=0.189 with a dominant central galaxy and numerous strongly-lensed features. Following our earlier papers, we combine strong and weak lensing constraints secured with Hubble Space Telescope and Subaru imaging with the radial profile of the stellar velocity dispersion of the central galaxy, essential for separating the baryonic mass distribution in the cluster core. Hydrostatic mass estimates from Chandra X-ray observations further constrain the solution. These combined datasets provide nearly continuous constraints extending from 2 kpc to 1.5 Mpc in radius, allowing stringent tests of results from recent numerical simulations. Two key improvements in our data and its analysis make this the most robust case yet for a shallow slope \beta of the DM density profile \rho_DM ~ r^-\beta on small scales. First, following deep Keck spectroscopy, we have secured the stellar velocity dispersion profile to a radius of 26 kpc for the first time in a lensing cluster. Secondly, we improve our previous analysis by adopting a triaxial DM distribution and axisymmetric dynamical models. We demonstate that in this remarkably well-constrained system, the logarithmic slope of the DM density at small radii is \beta < 1.0 (95% confidence). An improved treatment of baryonic physics is necessary, but possibly insufficient, to reconcile our observations with the recent results of high-resolution simulations.