The non-Gaussian Cold Spot in the 3-year WMAP data

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  • 31 March 2006
Abstract
The non-Gaussian cold spot detected in wavelet space in the WMAP 1-year data, is detected again in the coadded WMAP 3-year data at the same position (b = -57, l = 209) and size in the sky (around 10 degrees). The present analysis is based on several statistical methods: kurtosis, maximum absolute temperature, number of cold pixels below a given threshold, volume and Higher Criticism. All these methods detect deviations from Gaussianity in the 3-year data set at a slightly higher confidence level than in the WMAP 1-year data. These small differences are mainly due to the new foreground reduction technique and not to the reduction of the noise level, which is negligible at the scale of the spot. The probability of finding such a spot in Gaussian simulations is well below 1%. The frequency dependence of the spot is shown to be extremely flat. Galactic foreground emissions are not likely to be responsible for the detected deviation from Gaussianity.

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