Measuring line-of-sight shear with Einstein rings: a proof of concept

Understand

Line-of-sight effects in strong gravitational lensing have long been treated as a nuisance.

• However, it was recently proposed that the line-of-sight shear could be a cosmological observable in its own right, if it is not degenerate with lens model parameters.
• We firstly demonstrate that the line-of-sight shear can be accurately measured from a simple simulated strong lensing image with percent precision.
• We then extend our analysis to more complex simulated images and stress test the recovery of the line-of-sight shear when using deficient fitting models, finding that it escapes from degeneracies with lens model parameters, albeit at the expense of the precision.