Non-gaussianity in the foreground-reduced CMB maps

TL;DR

This study investigates the non-Gaussian features in full-sky foreground-reduced CMB maps from WMAP data, revealing significant deviations from Gaussianity that vary with foreground removal methods and the use of masks.

Contribution

It introduces and applies large-angle non-Gaussianity indicators based on skewness and kurtosis to analyze full-sky WMAP maps, highlighting the impact of foreground removal and masking on Gaussianity.

Findings

Full-sky foreground-reduced maps show significant non-Gaussianity.

Masking reduces non-Gaussianity levels, improving Gaussianity.

Different foreground-reduction procedures influence non-Gaussianity detection.

Abstract

[Abridged]: A detection or nondetection of primordial non-Gaussianity by using the CMB data is crucial not only to discriminate inflationary models but also to test alternative scenarios. Non-Gaussianity offers, therefore, a powerful probe of the physics of the primordial universe. The extraction of primordial non-Gaussianity is a difficult enterprise since several effects of non-primordial nature can produce non-Gaussianity. Most of the Gaussianity analyses of CMB data have been performed by using part-sky frequency, where masks are used to deal with the galactic diffuse foreground emission. However, full-sky map seems to be potentially more appropriate to test for Gaussianity of the CMB data. On the other hand, masks can induce bias in some non-Gaussianity analyses. Here we use two recent large-angle non-Gaussianity indicators, based on skewness and kurtosis of large-angle patches of CMB maps, to examine the question of non-Gaussianity in the available full-sky five-year and seven-year WMAP maps. We show that these full-sky foreground-reduced maps present a significant deviation from Gaussianity of different levels, which vary with the foreground-reducing procedures. We also make a Gaussianity analysis of the foreground-reduced five-year and seven-year WMAP maps with a KQ75 mask, and compare with the similar analysis performed with the full-sky foreground-reduced maps. This comparison shows a significant reduction in the levels of non-Gaussianity when the mask is employed, which provides indications on the suitability of the foreground-reduced maps as Gaussian reconstructions of the full-sky CMB.