Dark Matter in Galaxy Clusters: a Parametric Strong Lensing Approach
  We present a parametric strong lensing analysis of three massive clusters.
Our aim is to probe the inner shape of dark matter haloes, in particular the
existence of a core. We adopt the following working hypothesis: any
group/cluster scale dark matter clump introduced in the modelling should be
associated with a luminous counterpart. We also adopt some additional well
motivated priors in the analysis, even if this degrades the quality of the fit,
quantified using the RMS between the observed and model generated images. In
particular, in order to alleviate the degeneracy between the smooth underlying
component and the galaxy scale perturbers, we use the results from spectrocopic
campaigns by Bergamini et al. (2019) allowing to fix the mass of the galaxy
scale component. In the unimodal galaxy cluster AS1063, a cored mass model is
favored with respect to a non cored mass model. This is also the case in the
multimodal cluster MACSJ0416, but we consider that the RMS difference between
both models is not large enough to disentangle between a cored and a non cored
mass model. In the unimodal cluster MACSJ1206, we fail to reproduce the strong
lensing constraints using a parametric approach within the adopted working
hypothesis. We then sucessfully add a mild perturbation in the form of a
superposition of B-spline potentials which allows to get a decent fit
(RMS=0.5"), finally finding that a cored mass model is favored. Overall, our
analysis suggest evidence for cored cluster scale dark matter haloes. These
findings may be usefull to interpret within alternative dark matter scenario,
as self interacting dark matter. We propose a working hypothesis for parametric
strong lensing modelling where the quest for the best fit model will be
balanced by the quest for presenting a physically motivated mass model, in
particular by imposing priors.
