Strong Lensing as a Probe of the Mass Distribution Beyond the Einstein Radius. Mass & Light in SL2S J08544-0121, a Galaxy Group at z=0.35

TL;DR

This paper demonstrates how strong lensing can be used to probe the mass distribution of galaxy groups beyond the Einstein radius, revealing the connection between light and mass and constraining global properties of the group.

Contribution

It introduces a method to use strong lensing perturbations to infer external mass distributions and properties of galaxy groups, extending the utility of lensing analyses.

Findings

External mass perturbations can be accurately modeled using strong lensing data.

The group mass-to-light ratio is constrained to approximately 98+-27.

Weak lensing analysis supports the strong lensing derived mass-to-light ratio.

Abstract

Precise modelling of strong lensing systems can be affected by external mass distributions, e.g. the group or cluster within which the lens is embedded. In this article, we propose to turn this limitation to our advantage and to use precise strong lensing modelling to probe external mass distributions surrounding the lens. We consider SL2S J08544-0121, a galaxy group at z=0.35 that contains a strong lensing system. A simple elliptical isothermal potential cannot reproduce satisfactorily the strong lensing constraints. We include an external mass perturbation corresponding to the group within which the lens is embedded. The lensing properties of this perturbation are parametrised by its total mass M and a smoothing scale s that quantifies the characteristic scale over which M is distributed. For a range of these parameters, we are able to reproduce accurately the observations. This suggests that light is a good tracer of mass. Interestingly, this also shows that a localised strong lensing analysis (on scales of ~10") allows us to constrain global properties of the group as a whole (on scales of ~100). Indeed, we constrain the group mass-to-light ratio to be M/L=98+-27 (i band, solar units, not corrected for evolution) and s=20" +- 9 (2sigma confidence level). We demonstrate that these strong lensing only constraints are due to the perturbed strong lensing configuration, where the main arc is located at ~5" from the galaxy, whereas its counter-image is found at ~8". To test independently our resulting strong lensing model, we pursue an independent weak lensing analysis of the group and find a mass-to-light ratio in the range 66-146 (1sigma confidence level).