IMPROVED CONSTRAINTS ON PRIMORDIAL NON-GAUSSIANITY FOR THEWILKINSON MICROWAVE ANISOTROPY PROBE5-YEAR DATA

Abstract

We present constraints on the nonlinear coupling parameter f nl with the Wilkinson Microwave Anisotropy Probe (WMAP) data. We use an updated method based on the spherical Mexican hat wavelet (SMHW) which provides improved constraints on the f nl parameter. This paper is a continuation of a previous work by Curto et al., where several third-order statistics based on the SMHW were considered. In this paper, we use all the possible third-order statistics computed from the wavelet coefficient maps evaluated at 12 angular scales. The scales are logarithmically distributed from 6.9 arcmin to 500 arcmin. Our analysis indicates that f nl is constrained to –18 < f nl < +80 at 95% confidence level (CL) for the combined V+W WMAP map. This value has been corrected by the presence of undetected point sources, which adds a positive contribution of Δf nl = 6 ± 5. Our result excludes at ~99% CL the best-fitting value f nl = 87 reported by Yadav & Wandelt. We have also constrained f nl for the Q, V, and W frequency bands separately, finding compatibility with zero at 95% CL for the Q and V bands but not for the W band. We have performed some further tests to understand the cause of this deviation which indicate that systematics associated with the W radiometers could be responsible for this result. Finally, we have performed a Galactic north-south analysis for f nl. We have not found any asymmetry, i.e., the best-fitting f nl for the northern pixels is compatible with the best-fitting f nl for the southern pixels.