Non-Gaussian foreground residuals of the WMAP first-year maps

Abstract

We investigate the effect of foreground residuals in the WMAP (Wilkinson Microwave Anisotropy Probe) data by adding foreground contamination to Gaussian ensembles of cosmic microwave background (CMB) signal and noise maps. We evaluate a set of non‐Gaussian estimators on the contaminated ensembles to determine with what accuracy any residual in the data can be constrained using higher‐order statistics. We apply the estimators to the raw and cleaned Q‐, V‐ and W‐band first‐year maps. The foreground subtraction method applied to clean the data in Bennett et al. appears to have induced a correlation between the power spectra and normalized bispectra of the maps which is absent in Gaussian simulations. It also appears to increase the correlation between the Δℓ= 1 inter‐ℓ bispectrum of the cleaned maps and the foreground templates. In a number of cases the significance of the effect is above the 98 per cent confidence level.

Uncorrelated universe: Statistical anisotropy and the vanishing angular correlation function in WMAP years 1–3

“…Similarly, several novel methods proposed to study the statistical isotropy or Gaussianity of the CMB have also been introduced and discussed in the literature [36][37][38][39]. Here we focus on our previous studies [7,16], namely the alignment of the quadrupole and octopole with each other and with physical directions on the sky as revealed by the multipole vector formalism [18].…”

A new approach to probing primordial non-Gaussianity

“…Many studies involving primordial non‐Gaussianity have used the bispectrum, motivated by the fact that it contains all the information about f NL (Babich 2005). It has been extensively studied (Creminelli 2003; Komatsu, Spergel & Wandelt 2005; Cabella et al 2006; Creminelli et al 2006; Medeiros & Contaldo 2006; Liguori et al 2007; Smith, Senatore & Zaldarriaga 2009), with most of these measurements providing convolved estimates of the bispectrum. Optimized three‐point estimators were introduced by Heavens (1998), and have been successively developed (Smith, Zahn & Dore 2000; Komatsu et al 2005; Creminelli et al 2006; Smith & Zaldarriaga 2006; Creminelli, Senatore & Zaldarriaga 2007b) to the point where an estimator for f NL which saturates the Cramer–Rao bound exists for partial sky coverage and inhomogeneous noise (Smith et al 2009).…”

Adiabatic versus isocurvature non-Gaussianity

“…This form is motivated by the single-field inflation scenarios and then many models predict NG in terms of f NL (Bartolo et al 2004a). Optimized estimators of the bispectrum, which is the leading correlation term in the local form, are introduced by Heavens (1998) and have been successively developed to the point where an estimator for f NL saturates the Cramér-Rao bound for partial sky coverage and inhomogeneous noise (Komatsu, Spergel & Wandelt 2005;Cabella et al 2006;Creminelli et al 2006;Medeiros & Contaldi 2006;Smith & Zaldarriaga 2006;Creminelli, Senatore & Zaldarriaga 2007;Liguori et al 2007;Komatsu et al 2009;Smith, Senatore & Zaldarriaga 2009 (Arkani-Hamed et al 2004) predict large NG signals in equilateral configuration triangles ( 1 2 3 ), which is well described with equilateral-type f NL (Babich, Creminelli & Zaldarriaga 2004).…”