Supervoids in the WISE-2MASS catalogue imprinting Cold Spots in the Cosmic Microwave Background

TL;DR

This study links large supervoids identified in the WISE-2MASS galaxy catalog to Cold Spots in the CMB, suggesting supervoids may contribute to observed temperature decrements through secondary anisotropies.

Contribution

Develops spherically symmetric LTB supervoid models to explain CMB Cold Spots, highlighting the potential role of supervoids in secondary anisotropies and providing a new approach to understanding these features.

Findings

The Draco Supervoid can account for the CMB decrement via ISW and RS effects.

The Cold Spot's deep decrement is not fully explained by a supervoid alone.

Alignment probability between the Cold Spot and supervoids is low, indicating a possible causal link.

Abstract

The Cold Spot (CS) is a clear feature in the Cosmic Microwave Background (CMB); it could be of primordial origin, or caused by a intervening structure along the line of sight. We identified a large projected underdensity in the recently constructed WISE-2MASS all-sky infrared galaxy catalogue aligned with the Cold Spot direction at $(l,b)\approx(209^\circ,-57^\circ)$. It has an angular size of tens of degrees, and shows a $\sim20\%$ galaxy underdensity in the center. Moreover, we find another large underdensity in the projected WISE-2MASS galaxy map at $(l,b)\approx(101^\circ,46^\circ)$ (hereafter Draco Supervoid), also aligned with a CMB decrement, although less significant than that of the CS direction. Motivated by these findings, we develop spherically symmetric Lemaitre-Tolman-Bondi (LTB) compensated void models to explain the observed CMB decrements with these two underdensities, or "supervoids". Within our perturbative treatment of the LTB voids, we find that the Integrated Sachs-Wolfe and Riess-Sciama effects due to the Draco Supervoid can account for the CMB decrement observed in the same direction. On the contrary, the extremely deep CMB decrement in the CS direction is more difficult to explain by the presence of the CS supervoid only. Nevertheless, the probability of a random alignment between the CS and the corresponding supervoid is disfavored, and thus its contribution as a secondary anisotropy cannot be neglected. We comment on how the approximations used in this paper, in particular the assumption of spherical symmetry, could change quantitatively our conclusions and might provide a better explanation for the CMB CS.