Probing non-Gaussianities in the CMB on an incomplete sky using surrogates

TL;DR

This paper presents a Fourier-based method for generating surrogates from incomplete CMB data, enabling the detection of non-Gaussianities and asymmetries even with the Galactic plane masked, suggesting these anomalies are not solely due to foreground contamination.

Contribution

It introduces a novel approach transforming spherical harmonics into an orthonormal basis on the cut sky for surrogate generation in incomplete CMB data.

Findings

Non-Gaussianities and asymmetries are detectable despite masking the Galactic plane.

The Galactic plane is unlikely the main source of observed CMB anomalies.

Results support a violation of statistical isotropy in the CMB.

Abstract

We demonstrate the feasibility to generate surrogates by Fourier-based methods for an incomplete data set. This is performed for the case of a CMB analysis, where astrophysical foreground emission, mainly present in the Galactic plane, is a major challenge. The shuffling of the Fourier phases for generating surrogates is now enabled by transforming the spherical harmonics into a new set of basis functions that are orthonormal on the cut sky. The results show that non-Gaussianities and hemispherical asymmetries in the CMB as identified in several former investigations, can still be detected even when the complete Galactic plane (|b| < 30{\deg}) is removed. We conclude that the Galactic plane cannot be the dominant source for these anomalies. The results point towards a violation of statistical isotropy.