Directional Variations of the Non-Gaussianity Parameter f_NL

• Published in: The Astrophysical Journal
• Main Authors: RUDJORD O, HANSEN F. K, LAN X, MARINUCCI D, LIGUORI, MICHELE, MATARRESE, SABINO
• Other Authors: Rudjord, O, HANSEN F., K, Lan, X, Liguori, Michele, Marinucci, D, Matarrese, Sabino
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2010
• Subjects: South Pole; South pole
• Online Access: http://hdl.handle.net/11577/2426104; https://doi.org/10.1088/0004-637X/708/2/1321

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. 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 note 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 1%.