# Environmental effects on halo abundance and weak lensing peak statistics toward large underdense regions

## TL;DR

This study investigates how large underdense regions, like supervoids, influence halo counts and weak lensing peak statistics, revealing significant environmental effects that can help identify such cosmic structures.

## Contribution

The paper demonstrates that environmental effects significantly alter halo abundance and weak lensing peak statistics in large underdense regions, providing a new method to probe supervoids.

## Key findings

- Halo counts for massive haloes decrease in underdense regions
- Number of high peaks decreases, low peaks increase with underdensity
- Significant deviations (up to 5σ) in peak statistics indicate environmental effects

## Abstract

The cosmic microwave background (CMB) contains an anomalous cold spot with a surrounding hot ring, known as the Cold Spot. Inoue & Silk (2006) proposed that this feature could be explained by postulating a supervoid: if such a large underdense region exists, then the growth of matter perturbing around the spot might differ from the average value in the Universe and the differences might affect weak lensing analysis of peak statistics. To investigate environmental effects on halo number count and peak statistics, we used a publicly available ray-tracing simulation for a box size of 2250$h^{-1}$Mpc on a side (Takahashi et al. 2017). We found that the number counts for massive haloes toward the largest underdense region in the simulation decreases and the corresponding significance of the difference, based on a cosmic average, is $\geq3\sigma$. On the basis of the results of peak statistics analysis, the number of high peaks decreases with the decrement of massive haloes, but the number of low peaks increases with the lack of matter in the line of sight. The highest significance of the decrement in peak counts in large underdense regions is $5\sigma$ in the total signal-to-noise ratio. Our result implies that environmental effects on halo abundance and weak lensing peak statistic can be used to probe the presence and properties of supervoids.