Assessing the effects of foregrounds and sky removal in WMAP

Abstract

Many recent analyses have indicated that large scale WMAP data display anomalies that appear inconsistent with the standard cosmological paradigm. However, the effects of foreground contamination, which require elimination of some fraction of the data, have not been carefully investigated due to the complexity in the analysis. Here we develop a general formalism of how to incorporate these effects in any analysis of this type. Our approach is to compute the full multi-dimensional probability distribution function of all possible sky realizations that are consistent with the data and with the allowed level of contamination. As an example we apply this method to compute the joint probability distribution function for the possible realizations of quadrupole and octopole using the WMAP data. This 12 dimensional distribution function is explored using the Markov Chain Monte Carlo technique. The resulting chains are used to asses the statistical significance of the low quadrupole using frequentist methods, the quadrupole-octopole alignment using several methods (angular momentum dispersion, multipole vectors and a new method based of feature matching) and the quadrupole-octopole aligment with ecliptic.

12 pages, 11 figures, 3 tables; replaced with the version accepted by PRD. Added a few statistical tests and expanded discussion. Results unchanged. Added acknowledgement in v3, clarified discussion of other work in v4

References in corpus (11)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Preliminary Maps and Basic Results
• Asymmetries in the CMB anisotropy field
• A high resolution foreground cleaned CMB map from WMAP
• The significance of the largest scale CMB fluctuations in WMAP
• A Full-Sky H-alpha Template for Microwave Foreground Prediction
• Multipole Vectors--a new representation of the CMB sky and evidence for statistical anisotropy or non-Gaussianity at 2<=l<=8
• Asymmetries in the local curvature of the WMAP data
• A Maximum Likelihood Analysis of the Low CMB Multipoles from WMAP
• The Statistical Significance of the Low CMB Mulitipoles
• Exact likelihood evaluations and foreground marginalization in low resolution WMAP data

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