Probing supervoids with weak lensing

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.