Constraints on general primordial non-Gaussianity using wavelets for the Wilkinson Microwave Anisotropy Probe 7-year data

Abstract

We present constraints on the non-linear coupling parameter fnl with theWilkinson Microwave Anisotropy Probe (WMAP) data. We use the method based on the spherical Mexican hat wavelet to measure the fnl parameter for three of the most interesting shapes of primordial non-Gaussianity: local, equilateral and orthogonal. Our results indicate that this parameter is compatible with a Gaussian distribution within the 2σ confidence level (CL) for the three shapes and the results are consistent with the values presented by the WMAP team. We have included in our analysis the impact on fnl due to contamination by unresolved point sources. The point sources add a positive contribution of f loc nl = 2.5 ± 3.0, f eq nl = 37 ± 18 and f ort nl = 25 ± 14. As mentioned by the WMAP team, the contribution of the point sources to the orthogonal and equilateral forms is expected to be larger than the local one and thus it cannot be neglected in future constraints on these parameters. Taking into account this contamination, our best estimates for fnl are −16.0 ≤ f loc nl ≤ 76.0, −382 ≤ f eq nl ≤ 202 and −394 ≤ f ort nl ≤ 34 at 95 per cent CL. The three shapes are compatible with zero at 95 per cent CL (2σ). Our conclusion is that the WMAP 7-year data are consistent with Gaussian primordial fluctuations within 2σ CL. We stress however the importance of taking into account the unresolved point sources in the measurement of fnl in future works, especially when using more precise data sets such as the forthcoming Planck data.