Directional Variations of the Non-Gaussianity Parameter fₙL

الأصل · EN

We investigate local variations of the primordial non-Gaussianity parameter fₙL in the WMAP data, looking for possible influence of foreground contamination in the full-sky estimate of fₙL. We first improve the needlet bispectrum estimate in (Rudjord et al. 2009) on the full-sky to fₙL= 73 +/- 31 using the KQ75 mask on the co-added V+W channel. We find no particular values of fₙL estimates close to the galactic plane and conclude that foregrounds are unlikely to affect the estimate of fₙL in the V and W bands even for the smaller KQ85 mask. In the Q band however, we find unexpectedly high values of fₙL in local estimates close to the galactic mask, as well as significant discrepancies between Q band estimates and V/W band estimates. We therefore conclude that the Q band is too contaminated to be used for non-Gaussianity studies even with the larger KQ75 mask. We further noted that the local fₙL estimates on the V+W channel are positive on all equatorial bands from the north to the south pole. The probability for this to happen in a universe with fₙL = 0 is less than one percent.