Can a supervoid explain the Cold Spot?

Abstract

The discovery of a void of size $\sim 200h^{-1}$Mpc and average density contrast of $\sim -0.1$ aligned with the Cold Spot direction has been recently reported. It has been argued that, although the first-order integrated Sachs-Wolfe (ISW) effect of such a void on the CMB is small, the second-order Rees-Sciama (RS) contribution exceeds this by an order of magnitude and can entirely explain the observed Cold Spot temperature profile. In this paper we examine this surprising claim using both an exact calculation with the spherically symmetric Lemaître-Tolman-Bondi metric, and perturbation theory about a background Friedmann-Robertson-Walker (FRW) metric. We show that both approaches agree well with each other, and both show that the dominant temperature contribution of the postulated void is an unobservable dipole anisotropy. If this dipole is subtracted, we find that the remaining temperature anisotropy is dominated by the linear ISW signal, which is orders of magnitude larger than the second-order RS effect, and that the total magnitude is too small to explain the observed Cold Spot profile. We calculate the density and size of a void that would be required to explain the Cold Spot, and show that the probability of existence of such a void is essentially zero in $\Lambda$CDM. We identify the importance of \emph{a posteriori} selection effects in the identification of the Cold Spot, but argue that even after accounting for them, a supervoid explanation of the Cold Spot is always disfavoured relative to a random statistical fluctuation on the last scattering surface.

13 pages, 7 figures. Minor edits to match published version, 2 new references

References in corpus (15)

• An Imprint of Super-Structures on the Microwave Background due to the Integrated Sachs-Wolfe Effect
• Confronting Lemaitre-Tolman-Bondi models with Observational Cosmology
• The non-Gaussian Cold Spot in the 3-year WMAP data
• Extragalactic Radio Sources and the WMAP Cold Spot
• Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies I
• Scalar Perturbations on Lemaitre-Tolman-Bondi Spacetimes
• Local Voids as the Origin of Large-angle Cosmic Microwave Background Anomalies: The Effect of a Cosmological Constant
• The CMB cold spot: texture, cluster or void?
• Anti-lensing: the bright side of voids
• The stacked ISW signal of rare superstructures in ΛCDM
• CMB Lensing and the WMAP Cold Spot
• LTB solutions in Newtonian gauge: from strong to weak fields
• The Cold Spot as a Large Void: Rees-Sciama effect on CMB Power Spectrum and Bispectrum
• Cosmic Microwave Background Anisotropy from Nonlinear Structures in Accelerating Universes
• 21-cm Lensing and the Cold Spot in the Cosmic Microwave Background

Cited by in corpus (5)

• A detection of the integrated Sachs-Wolfe imprint of cosmic superstructures using a matched-filter approach
• Imprint of DES super-structures on the Cosmic Microwave Background
• Tracing the gravitational potential using cosmic voids
• Lensing in the Geodesic Light-Cone coordinates and its (exact) illustration to an off-center observer in Lemaître-Tolman-Bondi models
• On the Abundance of Extreme Voids