Testing light-traces-mass in Hubble Frontier Fields Cluster MACS-J0416.1-2403

TL;DR

This study reconstructs the mass distribution of galaxy cluster MACSJ0416 using a free-form method without light information, confirming light traces mass and highlighting differences with parametric models.

Contribution

It applies a novel free-form reconstruction technique to a complex cluster, providing insights into galaxy-mass correlations without relying on light data.

Findings

Light follows mass in the cluster.

Brighter galaxies are more strongly clustered with mass.

Discrepancies suggest galaxy bias varies between methods.

Abstract

We reconstruct the projected mass distribution of a massive merging Hubble Frontier Fields cluster MACSJ0416 using the genetic algorithm based free-form technique called Grale. The reconstructions are constrained by 149 lensed images identified by Jauzac et al. using HFF data. No information about cluster galaxies or light is used, which makes our reconstruction unique in this regard. Using visual inspection of the maps, as well as galaxy-mass correlation functions we conclude that overall light does follow mass. Furthermore, the fact that brighter galaxies are more strongly clustered with mass is an important confirmation of the standard biasing scenario in galaxy clusters. On the smallest scales, approximately less than a few arcseconds, the resolution afforded by 149 images is still not sufficient to confirm or rule out galaxy-mass offsets of the kind observed in ACO 3827. We also compare the mass maps of MACSJ0416 obtained by three different groups: Grale, and two parametric Lenstool reconstructions from the CATS and Sharon/Johnson teams. Overall, the three agree well; one interesting discrepancy between Grale and Lenstool galaxy-mass correlation functions occurs on scales of tens of kpc and may suggest that cluster galaxies are more biased tracers of mass than parametric methods generally assume.