New strong lensing modelling of SDSS J2222+2745 enhanced with VLT/MUSE spectroscopy

TL;DR

This study presents a detailed strong lensing model of SDSS J2222+2745 using HST imaging and VLT/MUSE spectroscopy, improving understanding of its mass distribution and highlighting the need for additional data for precise cosmological insights.

Contribution

The paper combines HST imaging with MUSE spectroscopy to create a more accurate lens model, including stellar kinematics, and discusses the impact of systematic uncertainties on mass estimates.

Findings

The mass distribution is best modeled with a large-scale component, galaxy-scale component, and external shear.

The model achieves a positional accuracy of 0.29 arcseconds for multiple images.

Magnification and time delay predictions are sensitive to local mass distribution details.

Abstract

SDSS J2222+2745, at z = 0.489, is one of the few currently known lens clusters with multiple images of a background (z = 2.801) quasar with measured time delays. We combine imaging from the Hubble Space Telescope (HST) with recent Multi Unit Spectroscopic Explorer (MUSE) spectroscopic data to securely identify 34 cluster members and 12 multiple images from 3 background sources. We measure the stellar velocity dispersions of 13 cluster galaxies, enabling an independent estimate of the contribution of the sub-halo mass component to the lens total mass. The projected total mass distribution of the lens cluster is best modelled with a single large-scale mass component, a galaxy-scale component, anchored by the MUSE kinematic information, and an external shear. The best-fit strong lensing model yields a root mean square separation between the model-predicted and observed positions of the multiple images of 0".29. When analysing the impact of systematic uncertainties, stemming from modelling assumptions and used observables, we find that the projected total mass profile, relative weight of the sub-halo mass component, and critical lines are consistent, within the statistical uncertainties. The predicted magnification and time delay values are, instead, more sensitive to the local details of the lens total mass distribution, and vary significantly among lens models that are similarly good at reproducing the observed multiple image positions. Due to its complex morphology, the low number of point-like multiple images, and current model degeneracies, it becomes clear that additional information (from the observed surface brightness distribution of lensed sources and the measured time delays) needs to be included in the modelling of SDSS J2222+2745 for accurate and precise cosmological measurements. The full MUSE secure spectroscopic catalogue presented in this work is made publicly available.