Shapley Supercluster Survey: mapping the dark matter distribution

TL;DR

This study uses weak gravitational lensing to map the dark matter distribution in the Shapley supercluster, revealing interconnected clusters, a filament, and background structures, and measuring their masses consistent with other methods.

Contribution

First comprehensive weak lensing survey of the Shapley supercluster core, mapping dark matter and confirming cluster interactions and filamentary structures.

Findings

Detected all clusters via lensing, correlating dark matter with galaxy density.

Mapped a coherent structure of five interacting clusters and a filament.

Measured cluster masses consistent with dynamical and X-ray data.

Abstract

We present a 23deg$^2$ weak gravitational lensing survey of the Shapley supercluster core and its surroundings using $gri$ VST images as part of the Shapley Supercluster Survey (ShaSS). This study reveals the overall matter distribution over a region containing 11 clusters at $z{\sim}0.048$ that are all interconnected, as well as several ongoing cluster-cluster interactions. Galaxy shapes have been measured by using the Kaiser-Squires-Broadhurst method for the $g$- and $r$-band images and background galaxies were selected via the $gri$ colour-colour diagram. This technique has allowed us to detect all of the clusters, either in the $g$-band or $r$-band images, although at different $\sigma$ levels, indicating that the underlying dark matter distribution is tightly correlated with the number density of the member galaxies. The deeper $r$-band images have traced the five interacting clusters in the supercluster core as a single coherent structure, confirmed the presence of a filament extending North from the core, and have revealed a background cluster at $z{\sim}0.17$. We have measured the masses of the four richest clusters (A3556, A3558, A3560 and A3562) in the two-dimensional shear pattern, assuming a spherical Navarro-Frenk-White (NFW) profile and obtaining a total mass of $\mathcal{M}_{\rm ShaSS,WL}{=}1.56^{+0.81}_{-0.55}{\times}10^{15\,}{\rm M}_{\odot}$, which is consistent with dynamical and X-ray studies. Our analysis provides further evidence of the ongoing dynamical evolution in the ShaSS region.