Line-of-sight structure of troughs identified in Subaru Hyper Suprime-Cam Year 3 weak lensing mass maps

TL;DR

This study investigates the line-of-sight structures of troughs identified in weak lensing mass maps from Subaru HSC data, revealing most are due to multiple voids, but some may originate from elongated single voids.

Contribution

It provides the first detailed analysis of the line-of-sight structure of weak lensing troughs, distinguishing between multiple voids and elongated single voids as their origins.

Findings

Most troughs are caused by multiple aligned voids.

Two troughs may originate from single elongated voids.

Elongated voids can produce weak lensing signals similar to multiple voids.

Abstract

We perform the weak lensing mass mapping analysis to identify troughs, which are defined as local minima in the mass map. Since weak lensing probes projected matter along the line-of-sight, these troughs can be produced by single voids or multiple voids projected along the line-of-sight. To scrutinise the origins of the weak lensing troughs, we systematically investigate the line-of-sight structure of troughs selected from the latest Subaru Hyper Suprime-Cam (HSC) Year 3 weak lensing data covering $433.48 \, \mathrm{deg}^2$. From a curved sky mass map constructed with the HSC data, we identify 15 troughs with the signal-to-noise ratio higher than $5.7$ and address their line-of-sight density structure utilizing redshift distributions of two galaxy samples, photometric luminous red galaxies observed by HSC and spectroscopic galaxies detected by Baryon Oscillation Spectroscopic Survey. While most of weak lensing signals due to the troughs are explained by multiple voids aligned along the line-of-sight, we find that two of the 15 troughs potentially originate from single voids at redshift $\sim 0.3$. The single void interpretation appears to be consistent with our three-dimensional mass mapping analysis. We argue that single voids can indeed reproduce observed weak lensing signals at the troughs if these voids are not spherical but are highly elongated along the line-of-sight direction.