Detection of a non-Gaussian spot in WMAP

2004/12/16 by M. Cruz, E. Martinez-Gonzalez, E. Martínez-González +3 · 342 citations
Physics and Astronomy · #Anisotropy #Astrophysics #Bright spot #CMB cold spot #Cosmic background radiation #Cosmic microwave background #Cosmology and Gravitation Theories #Gaussian #Hot spot (computer programming) #Kurtosis #Maxima and minima #Neutrino Physics Research #Non-Gaussianity #Optics #Particle physics theoretical and experimental studies #Physics #Planck #Sky #Spots #Statistics #Wavelet

paper · open access · doi:10.1111/j.1365-2966.2004.08419.x

published in Monthly Notices of the Royal Astronomical Society 356(1), 29-40 (Oxford University Press)

openalex publication_date 2004/12/16 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

An extremely cold and big spot in the Wilkinson Microwave Anisotropy Probe (WMAP) 1-yr data is analysed. Our work is a continuation of a previous paper by Vielva et al. that reported the detection of non-Gaussianity, with a method based on the spherical Mexican hat wavelet (SMHW) technique. We study the spots at different thresholds on the SMHW coefficient maps, considering six estimators, namely the number of maxima, the number of minima, the numbers of hot and cold spots, and the number of pixels of those spots. At SMHW scales around 4° (10° on the sky), the data deviate from Gaussianity. The analysis is performed on all of the sky, the Northern and Southern hemispheres, and on four regions covering all of the sky. A cold spot at (b=-57°, l= 209°) is found to be the source of this non-Gaussian signature. We compare the spots of our data with 10 000 Gaussian simulations, and conclude that only around 0.2 per cent of them present such a cold spot. Excluding this spot, the remaining map is compatible with Gaussianity, and even the excess of kurtosis in the paper by Vielva et al. is found to be due exclusively to this spot. Finally, we study whether the spot causing the observed deviation from Gaussianity could be generated by systematics or foregrounds. None of them seem to be responsible for the non-Gaussian detection.

Citations

• Testing the cosmological principle of isotropy: local power-spectrum estimates of theWMAPdata

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