Weak Lensing by Intergalactic Mini-Structures in Quadruple Lens Systems: Simulation and Detection

TL;DR

This study uses simulations to analyze how small intergalactic structures along the line of sight affect the magnification and positions of images in quadruple lens systems, providing new insights into dark matter distribution.

Contribution

It introduces a detailed simulation approach and a new analytical estimate for weak lensing effects of mini-structures in quadruple lens systems, aligning with observed flux ratios.

Findings

Magnification ratios change by about 10% due to line-of-sight structures.

Projected density perturbations are on the order of 10^8 solar masses per arcsec^2.

Flux perturbations are mainly caused by minivoids and minihalos in underdense regions.

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.