On the contribution of large scale structure to strong gravitational lensing

TL;DR

This study investigates how large-scale cosmic structures influence the occurrence and properties of strong gravitational lensing, using COSMOS data and simulations to analyze environmental effects on lensing phenomena.

Contribution

It provides new insights into the environmental dependence of strong lensing, highlighting discrepancies between observations and simulations, and emphasizes the need for improved detection methods.

Findings

Lensed images with large angular separations are found in dense regions.

The fraction of elliptical galaxies that are strong lenses is environment-independent in observations.

Simulations predict an increasing lens fraction in dense environments, contrary to observations.

Abstract

We study the correlation between the locations of galaxy-galaxy strong lensing candidates and tracers of large-scale structure from both weak lensing or X-ray emission. The COSMOS survey is a unique data set, combining deep, high resolution and contiguous imaging in which strong lenses have been discovered, plus unparalleled multiwavelength coverage. To help interpret the COSMOS data, we have also produced mock COSMOS strong and weak lensing observations, based on ray-tracing through the Millenium simulation. In agreement with the simulations, we find that strongly lensed images with the largest angular separations are found in the densest regions of the COSMOS field. This is explained by a prevalence among the lens population in dense environments of elliptical galaxies with high total-to-stellar mass ratios, which can deflect light through larger angles. However, we also find that the overall fraction of elliptical galaxies with strong gravitational lensing is independent of the local mass density; this observation is not true of the simulations, which predict an increasing fraction of strong lenses in dense environments. The discrepancy may be a real effect, but could also be explained by various limitations of our analysis. For example, our visual search of strong lens systems could be incomplete and suffer from selection bias; the luminosity function of elliptical galaxies may differ between our real and simulated data; or the simplifying assumptions and approximations used in our lensing simulations may be inadequate. Work is therefore ongoing. Automated searches for strong lens systems will be particularly important in better constraining the selection function.