Disks in the sky: A reassessment of the WMAP "cold spot"

Abstract

We reassess the evidence that WMAP temperature maps contain a statistically significant "cold spot" by repeating the analysis using simple circular top-hat (disk) weights, as well as Gaussian weights of varying width. Contrary to previous results that used Spherical Mexican Hat Wavelets, we find no significant signal at any scale when we compare the coldest spot from our sky to ones from simulated Gaussian random, isotropic maps. We trace this apparent discrepancy to the fact that WMAP cold spot's temperature profile just happens to favor the particular profile given by the wavelet. Since randomly generated maps typically do not exhibit this coincidence, we conclude that the original cold spot significance originated at least partly due to a fortuitous choice of using a particular basis of weight functions. We also examine significance of a more general measure that returns the most significant result among several choices of the weighting function, angular scale of the spot, and the statistics applied, and again find a null result. © 2009 Elsevier B.V. All rights reserved.