WMAP 5-year constraints on fnl with wavelets

TL;DR

This paper analyzes WMAP 5-year CMB data for non-Gaussianity using wavelet-based estimators, constraining the local non-linear coupling parameter fnl to be between -8 and 111, consistent with Gaussianity.

Contribution

It introduces a wavelet-based third order estimator approach to constrain fnl, providing results comparable to bispectrum analyses.

Findings

WMAP data are compatible with Gaussian simulations.

The constrained fnl range is -8 to 111 at 95% CL.

Results agree with previous bispectrum-based constraints.

Abstract

We present a Gaussianity analysis of the WMAP 5-year Cosmic Microwave Background (CMB) temperature anisotropy data maps. We use several third order estimators based on the spherical Mexican hat wavelet. We impose constraints on the local non-linear coupling parameter fnl using well motivated non-Gaussian simulations. We analyse the WMAP maps at resolution of 6.9 arcmin for the Q, V, and W frequency bands. We use the KQ75 mask recommended by the WMAP team which masks out 28% of the sky. The wavelet coefficients are evaluated at 10 different scales from 6.9 to 150 arcmin. With these coefficients we compute the third order estimators which are used to perform a chi-squared analysis. The chi-squared statistic is used to test the Gaussianity of the WMAP data as well as to constrain the fnl parameter. Our results indicate that the WMAP data are compatible with the Gaussian simulations, and the fnl parameter is constrained to -8 < fnl < +111 at 95% CL for the combined V+W map. This value has been corrected for the presence of undetected point sources, which add a positive contribution of Delta_fnl = 3+-5 in the V+W map. Our results are very similar to those obtained by Komatsu et al (2008) using the bispectrum.