Separating Baryons and Dark Matter in Cluster Cores: A Full Two‐dimensional Lensing and Dynamic Analysis of Abell 383 and MS 2137−23

Abstract

We utilize existing data for the galaxy clusters MS 2137–23 and Abell 383 to present improved measures of the distribution of dark and baryonic material in the clusters' central regions. Our method, based on the combination of gravitational lensing and dynamical data, is uniquely capable of separating the distribution of dark and baryonic components at scales below 100 kpc. Our mass models include pseudoelliptical generalized NFW profiles for constraining the inner dark matter slope. We find that a variety of strong-lensing models fit the available data, including some with dark matter profiles as steep as expected from recent simulations. However, when combined with stellar velocity dispersion data for the brightest member, shallower inner slopes than predicted by numerical simulations are preferred, in general agreement with our earlier work in these clusters. For Abell 383, the preferred shallow inner slopes are statistically a good fit only when the multiple-image position uncertainties associated with our lens model are assumed to be 0.5, to account for unknown substructure. No statistically satisfactory fit was obtained matching both the multiple-image lensing data and the velocity dispersion profile of the brightest cluster galaxy in MS 2137–23. This suggests that the mass model we are using, which comprises a pseudoelliptical generalized NFW profile and a brightest cluster galaxy component, may inadequately represent the inner cluster regions. This may arise due to halo triaxiality or by the gravitational interaction of baryons and dark matter in cluster cores. The progress made via this detailed study highlights the key role that complementary observations of lensed features and stellar dynamics offer in understanding the interaction between dark and baryonic matter on nonlinear scales in the central regions of clusters.