Testing Light Unaffiliated Mass Clumps in MACS 0416 on galaxy and galaxy cluster scales using JWST

TL;DR

This study uses JWST data to test the existence of light unaffiliated mass clumps in MACS 0416, finding that a model without such clumps can explain observations, supporting the association of dark matter with light in clusters.

Contribution

The paper demonstrates that parametric models without light unaffiliated mass clumps can fit strong lensing data, challenging previous non-parametric findings of such clumps.

Findings

A mass model with stellar counterparts reproduces all multiple images.

One galaxy-scale LUMC (M2) remains marginally significant but is not strongly favored.

Parametric and non-parametric models agree within 5-6% in mass distribution.

Abstract

Light unaffiliated mass clumps (LUMCs), i.e. dark matter (DM) components without any stellar counterparts, have been reported in strong lensing mass reconstructions of MACS 0416, both on galaxy and galaxy cluster scales. On galaxy cluster scale, the most recent parametric study based on 303 multiple images features a LUMC, in the south of the cluster. On galaxy scale, the most recent GRALE non-parametric study based on 237 multiple images features two LUMCs, M1 and M2. Given the implications of these findings in the context of structure formation and evolution, we test these features parametrically, using LENSTOOL. First, we show that a mass model where each large scale DM component introduced in the modelling is associated with a stellar counterpart can reproduce the 303 multiple images, removing the need for any cluster scale LUMC in \lens. We then update the GRALE model using the 303 multiple images, finding that one of the two galaxy scale LUMC, M1, is no longer significant, while M2 remains. We test M2 by explicitely including it in our parametric model. We find that the inclusion of this LUMC does not improve the global RMS, but mildly improves locally the RMS for one multiple image located close to M2. Besides, the preferred mass for M2 corresponds to the lowest mass allowed by the adopted prior. M2 is therefore not strongly favoured by a parametric approach but it is not ruled out. We present a comparison of parametric and non-parametric models in the M2 area. Both approaches show very similar surface mass density at this location, with a 5-6 % difference between the mass maps. The difference is that GRALE favors a distinct mass substructure when LENSTOOL favors a more diffuse mass distribution. We have been able to propose a parametric mass model without including any LUMCs, providing further evidences for DM being associated with light in clusters.