Directional Variations of the Non-Gaussianity Parameter f_NL

Abstract

We investigate local variations of the primordial non-Gaussianity parameter f_NL in the WMAP data, looking for possible influence of foreground contamination in the full-sky estimate of f_NL. We first improve the needlet bispectrum estimate in (Rudjord et al. 2009) on the full-sky to f_NL= 73 +/- 31 using the KQ75 mask on the co-added V+W channel. We find no particular values of f_NL estimates close to the galactic plane and conclude that foregrounds are unlikely to affect the estimate of f_NL in the V and W bands even for the smaller KQ85 mask. In the Q band however, we find unexpectedly high values of f_NL 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 f_NL 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 f_NL = 0 is less than one percent.

6 pages, 2 figures, included section on non-Gaussian maps, references added

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• BOOMERanG Constraints on Primordial Non-Gaussianity from Analytical Minkowski Functionals
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• Constraints on general primordial non-Gaussianity using wavelets for the Wilkinson Microwave anisotropy probe 7-year data
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• High-frequency asymptotics for Lipschitz-Killing curvatures of excursion sets on the sphere
• Foreground influence on primordial non-Gaussianity estimates: needlet analysis of WMAP 5-year data
• Needatool: A Needlet Analysis Tool for Cosmological Data Processing
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• Wilkinson Microwave Anisotropy Probe 7-yr constraints on fNL with a fast wavelet estimator
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