Dark matter in galaxy clusters: Parametric strong-lensing approach

Abstract

Context. We present a parametric strong-lensing analysis of three massive galaxy clusters for which Hubble Space Telescope imaging is available, as well as spectroscopy of multiply imaged systems and galaxy cluster members. Our aim is to probe the inner shape of dark matter haloes, in particular the existence of a core. We adopted the following working hypothesis: any group-or cluster-scale dark matter clump introduced in the modelling should be associated with a luminous counterpart. We also adopted some additional well-motivated priors in the analysis, even when this degraded the quality of the fit, quantified using the root mean square 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 used the results from previous spectroscopic campaigns, which allowed us to fix the mass of the galaxy-scale component. In the unimodal galaxy cluster AS 1063, a core mass model is favoured over a non-core mass model, and this is also the case in the multimodal cluster MACS J0416. In the unimodal cluster MACS J1206, we fail to reproduce the strong-lensing constraints using a parametric approach within the adopted working hypothesis. We then successfully added a mild perturbation in the form of a superposition of B-spline potentials, which allowed us to obtain a decent fit (root mean square = 0.5 ′′ ), and finally find that a core mass model is favoured. Overall, our analysis suggest evidence for core cluster-scale dark matter haloes in these three clusters. These findings may be useful for the interpretation within alternative dark matter scenario, such as self-interacting dark matter. We propose a working hypothesis for parametric strong-lensing modelling in which the quest for the best-fit model is balanced by the quest for presenting a physically motivated mass model, in particular by imposing priors. Aims.Methods. Results. Gravitational lensing: strong lensing -Galaxies: cluster -Conclusions.

CLASH-VLT: The Inner Slope of the MACS J1206.2-0847 Dark Matter Density Profile

“…Of the two values, one is given without an error estimate (Manjón-García et al 2020) and the other is zero, and significantly smaller than the NFW value (S04). The result of S04 is supported by the strong lensing analysis of Limousin et al (2022), who find that a cored inner mass density profile is a better fit to the data than a cuspy model.…”

“…They found that a cored DM halo reproduces the observed kinematics better than an NFW profile. Based on a strong lensing analysis of three clusters, Limousin et al (2022) find that cored inner mass density profiles are favored over cuspy models. Using a combination of strong gravitational lensing and BCG kinematics, Newman et al (2013b) estimate γ DM = 0.50 ± 0.13 averaging over seven clusters, in agreement with previous results by the same collaboration (Sand et al 2002(Sand et al , 2008Newman et al 2009Newman et al , 2011.…”

“…Given the rather extreme γ DM value measured for MACS 1206 by S04, and supported by the analysis of Limousin et al (2022), it is interesting to have a new, independent determination of it with a kinematic data set of superior quality. In this paper, we apply the procedure of Sartoris et al (2020) to our new data for the cluster galaxy redshifts and the BCG velocity dispersion profile, that come from the CLASH-VLT ESO Large Program (D 186.A-0798, P.I.…”

Strong gravitational lensing's `external shear' is not shear

“…Perhaps the model could have both a4 and b4 perturbations, varying as a function of radius. Cluster-scale models frequently use a soft core inside some scale radius, and (Limousin et al 2022) add B-spline functions. The number of free parameters must be balanced with the information available: pixellated mass models are generally underconstrained (and although they might be able to fit observations without external shear; Valls-Gabaud et al 2006, some lineof-sight shear is expected for galaxy-scale lenses).…”

“…Subsequent papers have even proposed using external shear as relatively high signal-to-noise measurements of the 'cosmic' shear along individual lines of sight (Birrer et al 2017;Desprez et al 2018;Kuhn et al 2020;Fleury et al 2021;Hogg et al 2022). However, the best-fit values of external shear did not match the lines of sight to the three other galaxies studied by Wong et al (2011) -and, in general, best-fit values are much larger than expected for both galaxy lenses (Keeton et al 1997;Witt & Mao 1997;Hilbert et al 2007;Suyu et al 2010;Barrera et al 2021) and cluster lenses (Robertson et al 2020;Limousin et al 2022). Using mock observations, Cao et al (2022, hereafter C22) demonstrated that the best-fit shear can be incorrect if the model of the mass distribution is missing complexity.…”