Non-Gaussian signatures in the temperature fluctuation observed by the Wilkinson Microwave Anisotropy Probe

Abstract

We present results from a test for the Gaussianity of the whole sky\nsub-degree scale CMB temperature anisotropy measured by the Wilkinson Microwave\nAnisotropy Probe (WMAP). We calculate the genus from the foreground-subtracted\nand Kp0-masked WMAP maps and measure the genus shift parameters defined at\nnegative and positive threshold levels and the asymmetry parameter to quantify\nthe deviation from the Gaussian relation. At WMAP Q, V, and W bands, the genus\nand genus-related statistics imply that the observed CMB sky is consistent with\nGaussian random phase field. However, from the genus measurement on the\nGalactic northern and southern hemispheres, we have found two non-Gaussian\nsignatures at the W band resolution (0.35 degree scale), i.e., the large\ndifference of genus amplitudes between the north and the south and the positive\ngenus asymmetry in the south, which are statistically significant at 2.6 sigma\nand 2.4 sigma levels, respectively. The large genus amplitude difference also\nappears in the WMAP Q and V band maps, deviating the Gaussian prediction with a\nsignificance level of about 2 sigma. The probability that the genus curves show\nsuch a large genus amplitude difference exceeding the observed values at all Q,\nV, and W bands in a Gaussian sky is only 1.4%. Such non-Gaussian features are\nreduced as the higher Galactic cut is applied, but their dependence on the\nGalactic cut is weak. We discuss possible sources that can induce such\nnon-Gaussian features, and conclude that the CMB data with higher\nsignal-to-noise ratio and the accurate foreground model are needed to\nunderstand the non-Gaussian signatures.\n