Detection of a Supervoid Aligned with the Cold Spot of the Cosmic Microwave Background

TL;DR

This study identifies a large supervoid aligned with the Cosmic Microwave Background Cold Spot, suggesting it could explain the Cold Spot through gravitational effects in the context of the Lambda-CDM model.

Contribution

First detection of a supervoid aligned with the Cold Spot using combined infrared and optical galaxy data, supporting its role in the Cold Spot phenomenon.

Findings

Identified a supervoid of radius ~220 Mpc/h at z~0.22.

Detected significant underdensity with >5 sigma significance.

Supervoid's properties are consistent with causing the Cold Spot.

Abstract

We use the WISE-2MASS infrared galaxy catalog matched with Pan-STARRS1 (PS1) galaxies to search for a supervoid in the direction of the Cosmic Microwave Background Cold Spot. Our imaging catalog has median redshift $z\simeq 0.14$, and we obtain photometric redshifts from PS1 optical colours to create a tomographic map of the galaxy distribution. The radial profile centred on the Cold Spot shows a large low density region, extending over 10's of degrees. Motivated by previous Cosmic Microwave Background results, we test for underdensities within two angular radii, $5^\circ$, and $15^\circ$. The counts in photometric redshift bins show significantly low densities at high detection significance, $\gtrsim 5 \sigma$ and $\gtrsim 6 \sigma$, respectively, for the two fiducial radii. The line-of-sight position of the deepest region of the void is $z\simeq 0.15-0.25$. Our data, combined with an earlier measurement by Granett et al. 2010, are consistent with a large $R_{\rm void}=(220 \pm 50) h^{-1}Mpc $ supervoid with $\delta_{m} \simeq -0.14 \pm 0.04$ centered at $z=0.22\pm0.03$. Such a supervoid, constituting at least a $\simeq 3.3\sigma$ fluctuation in a Gaussian distribution of the $\Lambda CDM$ model, is a plausible cause for the Cold Spot.