Day 1458

Thursday.


1808.09516
Magnification bias in the shear-ratio test: a viable mitigation strategy
Unruh, Schneider, Hilbert

Using the same lens galaxies, the ratios of tangential shears for different source galaxy redshifts is equal to the ratios of their corresponding angular-diameter distances.  This is the so-called shear-ratio test (SRT) and it is valid when effects induced by the intervening large-scale structure (LSS) an be neglected.  The dominant LSS effect is magnification bias which, on the one hand, induces an additional shear, and on the other hand, causes a magnification of the lens population.  The objective is to quantify the magnification bias for the SRT and show an easy-to-apply mitigation strategy that does not rely on additional observations.  Use ray-tracing data through the Millennium simulations to measure the influence of magnification on the SRT an test the mitigation strategy.  Using the SRT as a null-test, find deviations from zero up to 10% for a flux-limited sample of lens galaxies, which is a strong function of lens redshift and the lens-source line-of-sight separation.  Using the mitigation strategy can improve the null-test by a factor of ~100.