Hubble Frontier Field Free-Form Mass Mapping of the Massive Multiple-Merging Cluster MACSJ0717.5+3745

TL;DR

This study uses a free-form mass mapping technique on Hubble Frontier Fields data to accurately reconstruct the dark matter distribution in the complex, merging galaxy cluster MACSJ0717.5+3745, revealing multiple substructures and their relation to luminous matter.

Contribution

The paper introduces an improved free-form mass mapping method that doubles the constraints and refines dark matter distribution reconstruction in a highly irregular, massive merging cluster.

Findings

Identified multiple new sets of multiple images.

Reconstructed dark matter map with four distinct concentrations.

Discovered a significant offset between dark matter and luminous/X-ray peaks.

Abstract

We examine the latest data on the cluster MACSJ0717.5+3745 from the Hubble Frontier Fields campaign. The critically lensed area is the largest known of any lens and very irregular making it a challenge for parametric modelling. Using our Free-Form method we obtain an accurate solution, identify here many new sets of multiple images, doubling the number of constraints and improving the reconstruction of the dark matter distribution. Our reconstructed mass map shows several distinct central substructures with shallow density profiles, clarifying earlier work and defining well the relation between the dark matter distribution and the luminous and X-ray peaks within the critically lensed region. Using our free-form method, we are able to meaningfully subtract the mass contribution from cluster members to the deflection field to trace the smoothly distributed cluster dark matter distribution. We find 4 distinct concentrations, 3 of which are coincident with the luminous matter. The fourth peak has a significant offset from both the closest luminous and X-ray peaks. These findings, together with dynamical data from the motions of galaxies and gas will be important for uncovering the potentially important implications of this extremely massive and intriguing system.