The hot and cold spots in five-year WMAP data

Abstract

We present an extensive frequentist analysis of the one-point statistics (number, mean, variance, skewness and kurtosis) and two-point correlation functions determined for the local extrema of the cosmic microwave background temperature field observed in five-years of Wilkinson Microwave Anisotropy Probe (WMAP) data. Application of a hypothesis test on the one-point statistics indicates a low variance of hot and cold spots in all frequency bands of the WMAP data. The consistency of the observations with Gaussian simulations of the best-fitting cosmological model is rejected at the 95 per cent confidence level outside the WMAP KQ75 mask and the Northern hemispheres in the Galactic and ecliptic coordinate frames. We demonstrate that it is unlikely that residual Galactic foreground emission contributes to the observed non-Gaussianities. However, the application of a high-pass filter that removes large angular scale power does improve the consistency with the best-fitting cosmological model. Two-point correlation functions of the local extrema are calculated for both the temperature pair product [temperature-temperature (T-T)] and spatial pair-counting [point-point (P-P)]. The T-T observations demonstrate weak correlation on scales below 20° and lie completely below the lower 3σ confidence region once various temperature thresholds are applied to the extrema determined for the KQ75 mask and northern sky partitions. The P-P correlation structure corresponds to the clustering properties of the temperature extrema, and provides evidence that it is the large angular-scale structures, and some unusual properties thereof, that are intimately connected to the properties of the hot and cold spots observed in the WMAP five-year data. © 2009 RAS.