Survey of Gravitationally-lensed Objects in HSC Imaging (SuGOHI). II. Environments and Line-of-Sight Structure of Strong Gravitational Lens Galaxies to z ~ 0.8

TL;DR

This study analyzes the environments of strong gravitational lens galaxies up to redshift 0.8, finding they are generally in overdense regions locally, but their line-of-sight structures are similar to random fields once local galaxies are accounted for.

Contribution

It provides a comprehensive analysis of the local and line-of-sight environments of lens galaxies using new and existing data, including the discovery of 41 new lens candidates.

Findings

Lens fields are overdense locally compared to control fields.

Line-of-sight structures are consistent with random fields after removing local lens environment.

No significant evolution of lens environment overdensity with redshift.

Abstract

We investigate the local and line-of-sight overdensities of strong gravitational lens galaxies using wide-area multiband imaging from the Hyper Suprime-Cam Subaru Strategic Program. We present 41 new definite or probable lens candidates discovered in Data Release 2 of the survey. Using a combined sample of 87 galaxy-scale lenses out to a lens redshift of $z_{\mathrm{L}} \sim 0.8$, we compare galaxy number counts in lines of sight toward known and newly-discovered lenses in the survey to those of a control sample consisting of random lines of sight. We also compare the local overdensity of lens galaxies to a sample of "twin" galaxies that have a similar redshift and velocity dispersion to test whether lenses lie in different environments from similar non-lens galaxies. We find that lens fields contain higher number counts of galaxies compared to the control fields, but this effect arises from the local environment of the lens. Once galaxies in the lens plane are removed, the lens lines of sight are consistent with the control sample. The local environments of the lenses are overdense compared to the control sample, and are slightly overdense compared to those of the twin sample, although the significance is marginal. There is no significant evidence of the evolution of the local overdensity of lens environments with redshift.