Signals of Statistical Anisotropy in WMAP Foreground-Cleaned Maps

TL;DR

This paper applies a symmetry-based method to WMAP foreground-cleaned maps to detect statistical anisotropy, revealing significant signals that could stem from residual foregrounds, instrumental effects, or cosmological origins.

Contribution

It introduces a novel symmetry-based approach to test for statistical isotropy in CMB maps and applies it to WMAP data, uncovering anisotropy signals.

Findings

Detected statistically significant anisotropy signals in some WMAP maps.

Estimated residual foreground contamination levels in the cleaned maps.

Found an improbable degree of isotropy in W band maps, possibly due to noise modeling issues.

Abstract

Recently a symmetry-based method to test for statistical isotropy of the cosmic microwave background was developed. We apply the method to template-cleaned 3-year and 5-year WMAP-$DA$ maps. We examine a wide range of angular multipoles from $2 < l < 300$. The analysis detects statistically signicant signals of anisotropy inconsistent with an isotropic CMB in some of the foreground cleaned maps. We are unable to resolve whether the anomalies have a cosmological, local astrophysical or instrumental origin. Assuming the anisotropy arises due to residual foreground contamination, we estimate the residual foreground power in the maps. For the W band maps, we also find a highly improbable degree of isotropy we cannot explain. We speculate that excess isotropy may be caused by faulty modeling of detector noise.