| Strong Lensing as a Probe of the Mass Distribution Beyond the Einstein Radius. Mass & Light in SL2S J0544-0121, a Galaxy Group at z=0.35 (2009) | |||||||||
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| A precise modelling of a strong lensing system can be affected by some external mass distribution. In this article, we propose to turn this bother to our advantage and to use precise strong lensing modelling to probe the external mass distribution within which the lens is embedded. We consider SL2S J08544-0121, a galaxy group at z=0.35 which contains a strong lensing system. An elliptical isothermal potential is unable to reproduce satisfactorily the strong lensing constraints. We consider an external mass perturbation corresponding to the group within which the lens is embedded, drawn from the luminosity distribution of the group. The lensing properties of this perturbation depends on the amount of mass M it contains and a smoothing scale s. For a range of these parameters, we are able to accurately reproduce the observations. This suggests that light is a good tracer of the mass. Interestingly, this shows that a local strong lensing modelling (on scales of ~10") allows 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 between 52 and 165 and s < 40". 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 populating the deflector, whereas its counterimage is found at ~8". From an independent weak lensing analysis of the group and find a mass-to-light ratio between 66 and 146. We conclude that strong lensing can be used to probe mass distributions beyond the Einstein radius, and we characterise the kind of perturbed strong lensing systems allowing such an analysis: a non dominant strong lensing system used as a particle test probing the main potential. [ABRIDGED]. Comment: submitted to A&A. Comments welcome | |||||||||
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