Directional Variations of the Non-Gaussianity Parameter f_NL

• Published in: The Astrophysical Journal
• Main Authors: Rudjord, O, Hansen, F, Lan, X, Liguori, M, Matarrese, S., MARINUCCI, DOMENICO
• Other Authors: Marinucci, D, Matarrese, S
• Format: Article in Journal/Newspaper
• Language: English
• Published: University of Chicago Press 2010
• Subjects: cosmic microwave background – cosmology: observations – methods: statistical; Settore MAT/06 - PROBABILITA' E STATISTICA MATEMATICA; South pole
• Online Access: http://hdl.handle.net/2108/10353; https://doi.org/10.1088/0004-637X/708/2/1321; http://iopscience.iop.org/0004-637X/708/2/1321

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. 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 note 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 1%.