Probing supervoids with weak lensing

TL;DR

This paper investigates the detectability of supervoids associated with the Cold Spot in the CMB using weak lensing signals, demonstrating that upcoming surveys could identify such structures without stacking.

Contribution

The study uses full-sky ray-tracing simulations to show that supervoids of specific size and density contrast can be detected via weak lensing with high significance in current and future surveys.

Findings

Lensing signals from supervoids can reach S/N~3 in ΛCDM models.

Upcoming surveys could detect supervoids with S/N > 4 without stacking.

Tangential shear profiles constrain supervoid mass distribution.

Abstract

The cosmic microwave background (CMB) has non-Gaussian features in the temperature fluctuations. An anomalous cold spot surrounded with a hot ring, called the Cold Spot is one of such features. If a large underdence region (supervoid) resides towards the Cold Spot, we would be able to detect a systematic shape distortion in the images of background source galaxies via weak lensing effect. In order to estimate the detectability of such signals, we used the data of $N$-body simulations to simulate full-sky ray-tracing of source galaxies. We searched for a most prominent underdense region using the simulated convergence maps smoothed at a scale of 20 degree and obtained tangential shears around it. The lensing signal expected in a concordant $\Lambda$CDM model can be detected at a signal-to-noise ratio $S/N\sim3$. If a supervoid with a radius of $\sim 200\,h^{-1}\,\textrm{Mpc}$ and a density contrast $\delta_0 \sim -0.3$ at the centre resides at a redshift $z\sim 0.2$, on-going and near-future weak gravitational lensing surveys would detect a lensing signal with $S/N\gtrsim4$ without resorting to stacking. From the tangential shear profile, we can obtain a constraint on the projected mass distribution of the supervoid.