Departure from Gaussianity of the Cosmic Microwave Background Temperature Anisotropies in the Three-year Wmap Data

We test the hypothesis that the temperature of the cosmicmicrowave background is consistent with a Gaussian random field defined on the celestial sphere, using the full sky debiased internal linear combination (DILC) map produced from the three-yearWMAP data. We test the phases for spherical harmonic modes with ‘ 10 (which should be the cleanest) for uniformity, randomness, and correlation with phases of the foreground maps. The phases themselves are consistent with a uniform distribution, but the differences between phases (randomness) are not consistent with uniformity. For ‘ 1⁄4 3 and ‘ 1⁄4 6, the phases of the CMB maps cross-correlate with the foregrounds, suggesting the presence of residual contamination in the DILC map even on these large scales. We also use a one-dimensional Fourier representation to assemble a‘m into the T‘(’) for each ‘mode and test the positions of the resulting maxima and minima for consistency with uniformity randomness on the unit circle. The results show significant departures at the 0.5% level, with the one-dimensional peaks concentrated around’ 1⁄4 180 . This strongly significant alignment with the Galactic meridian, together with the cross-correlation of DILC phases with the foreground maps, strongly suggests that even the lowest spherical harmonic modes in the map are significantly contaminated with foreground radiation. Subject headinggs: cosmic microwave background — cosmology: observations — methods: data analysis