Wilkinson Microwave Anisotropy Probe 5-year constraints on f_NL with wavelets

We present a Gaussianity analysis of the Wilkinson Microwave Anisotropy Probe (WMAP) 5-yr 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 6.9arcmin for the Q, V, and W frequency bands. We use the KQ75 mask recommended by the WMAP team which masks out 28 per cent of the sky. The wavelet coefficients are evaluated at 10 different scales from 6.9 to 150arcmin. With these coefficients, we compute the third order estimators which are used to perform a χ2 analysis. The χ2 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 per cent confidence level (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 Δfnl = 3 +/- 5 in the V + W map. Our results are very similar to those obtained by the WMAP team using the bispectrum.