Supervoids in the WISE–2MASS catalogue imprinting cold spots in the cosmic microwave background

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) ≈ (209 • , −57 • ). It has an angular size of tens of degrees, and shows a ∼ 20% galaxy underdensity in the center. Moreover, we find another large underdensity in the projected WISE-2MASS galaxy map at (l, b) ≈ (101 • , 46 • ) (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.

Probing supervoids with weak lensing

“…Compared with the fitting results, in addition, the measured density contrast in Finelli et al (2016) is 1 − 5 times larger than that in our simulation. Since the tangential shear is proportional to the density contrast, and the amplitude of it depends on the redshifts of source galaxies and a supervoid, the lensing signals can be detected at S/N 4 at an angular distance between 10 and 35 degrees in on-going and future weak lensing observations.…”

“…Assuming the best-fitted supervoid model in Finelli et al (2016), it is effective to observe an annulus region around θ = 20 degrees for detecting the lensing signals since the tangential shear of an underdence region is maximized at θ = 20 degrees on a sky-plane with respect to the centre of the void. Compared with the fitting results, in addition, the measured density contrast in Finelli et al (2016) is 1 − 5 times larger than that in our simulation.…”

Excessive Shift of the CMB Acoustic Peaks of the Cold Spot Area

“…The combination of large synchronous shifts in acoustic peaks and lower than usual temperature at the Cold Spot area results in a 4.73σ detection (significance p 1.11 × 10 −6 ) against the ΛCDM model. And it was already reported in Finelli et al (2016) that in the WISE-2MASS galaxy catalog at z < 0.3 the Cold Spot region is surrounded by surprisingly large underdense regions around 15 • in radius, which are found to be in the same square patch. Thus we propose there is some extra localized unknown energy to stretch out the space in the transverse direction around the Cold Spot area to simultaneously account for the Cold Spot, the excessive shift of the acoustic peaks, and the large underdense regions.…”

Planck2015 results

“…However, several non-standard physical mechanisms have been proposed as possible explanations. These include the gravitational effect produced by a collapsing cosmic texture (Cruz et al 2007), the linear and nonlinear ISW effect caused by a void in the large-scale structure (e.g., Tomita 2005;Inoue & Silk 2006;Rudnick et al 2007;Tomita & Inoue 2008;Finelli et al 2016), a cosmic bubble collision within the eternal inflation framework (Czech et al 2010;Feeney et al 2011;McEwen et al 2012), and a localized version of the inhomogeneous reheating scenario within the inflationary paradigm (Bueno Sanchez 2014).…”