Mass & Light in Galaxy Clusters: Parametric Strong Lensing Approach

TL;DR

This paper revisits parametric strong lensing models of galaxy clusters, emphasizing the importance of physically motivated dark matter components, and highlights the limitations and potential misinterpretations of traditional modeling approaches.

Contribution

It introduces a physically motivated dark matter modeling approach that associates dark matter clumps with luminous counterparts, improving the realism of galaxy cluster mass models.

Findings

Inner dark matter profiles are flat in studied clusters.

A four-clump model is necessary for sub-arcsecond accuracy in Abell 370.

Total mass distribution aligns with stellar distribution to first order.

Abstract

Parametric strong lensing studies of galaxy clusters often display misleading features: group/cluster scale dark matter components without any stellar counterpart, offsets between both components larger than what might be allowed by neither Cold Dark Matter nor self interacting Dark Matter models, or significant unexplained external shear components. I am revisiting mass models where such misleading (and interesting) features have been reported, adopting the following working hypothesis: any group or cluster scale dark matter clump introduced in the modelling should be associated with a luminous counterpart, and any well motivated and reliable prior should be considered, even when this degrades the fit. The goal is to derive a physically motivated description of the dark matter component which might be compared to theoretical expectations. I succeed doing so in galaxy clusters AS 1063, MACS J0416 and MACS J1206, finding that the shape of the inner dark matter component has a flat density profile. These findings may be useful for the interpretation within dark matter scenario, such as self-interacting dark matter. I fail in Abell 370: a three dark matter clumps mass model (each clump being associated with its stellar counterpart) is unable to reproduce the observational constraints with a precision smaller than 2.3 arcsec. In order to provide a sub arcsec precision, I need to describe the dark matter distribution using a four dark matter clumps model, as found in earlier works. Examining the total projected mass maps, I however find a good agreement between the total mass and the stellar distribution in Abell 370, both being, to first order, bimodal. I interpret the misleading features as being symptomatic of the lack of realism of a parametric description of the dark matter distribution. I encourage caution and criticism on the outputs of parametric strong lensing modelling.