Weak lensing by intergalactic ministructures in quadruple lens systems: simulation and detection

Abstract

We investigate the weak lensing effects of line-of-sight structures on quadruple images in quasar-galaxy strong lens systems based on N-body and ray-tracing simulations that can resolve halos with a mass of 10^5 solar mass. The intervening halos and voids disturb the magnification ratios of lensed images as well as their relative positions due to lensing. The magnification ratios typically change by O(10%) when the shifts of relative angular positions of lensed images are constrained to <0.004 arcsec. The constrained amplitudes of projected density perturbations due to line-of-sight structures are O(10^8) solar mass per arcsec^2. These results are consistent with our new analytical estimate based on the two-point correlation of density fluctuations. The observed mid-infrared (MIR) flux ratios for 6 quasar-galaxy lens systems with quadruple images agree well with the numerically estimated values without taking into account of subhalos residing in the lensing galaxies. We find that the constrained mean amplitudes of projected density perturbations in the line-of-sight are negative, which suggests that the fluxes of lensed images are perturbed mainly by minivoids and minihalos in underdense regions. We derive a new fitting formula for estimating the probability distribution function of magnification perturbation. We also find that the mean amplitude of magnification perturbation roughly equals the standard deviation regardless of the model parameters.