Non-Gaussian Signatures in the Temperature Fluctuation Observed by the WMAP
Abstract
We present results from the test of Gaussianity of the whole sky sub-degree scale CMB temperature anisotropy measured by the WMAP. We calculate the genus from the foreground-subtracted WMAP maps and measure the genus shift parameters defined at negative and positive threshold levels (\Delta\nu_{-/+}) and the asymmetry parameter to quantify the deviation from the Gaussian relation. At WMAP Q, V, and W bands, the genus shows positive \Delta\nu_{-}, a non-Gaussian feature that is significant at about 2 sigma level, while the \Delta\nu_{+} is consistent with zero. The probability that the genus curves show positive \Delta\nu_{-}'s exceeding the observed values and the zero-consistent \Delta\nu_{+}'s at all bands in a Gaussian sky is only 1%. We have found that the \Delta\nu_{-} increases as the smoothing scale increases, and as the lower Galactic cut is applied. However, the \Delta\nu_{+} does not show any noticeable dependence on the smoothing scale or the Galactic cut. Although the dependence of \Delta\nu_{-} on the Galactic cut implies that the Galactic foregrounds are the source for the non-Gaussianity, the observed genus shift pattern is quite different from that expected in the presence of the Galactic foregrounds. By comparing the genus in the Galactic north and south hemispheres, we have detected another non-Gaussian signature, i.e., the large difference of genus amplitudes between the north and the south and the positive genus asymmetry in the south, which is statistically significant at 2.9 sigma and 2.4 sigma levels, respectively. We discuss possible sources that can induce such non-Gaussian features, and conclude that the CMB data with higher signal-to-noise ratio and the accurate foreground model are needed to understand the non-Gaussian signatures. [abridged]Keywords
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