Probing foreground residuals in cleaned CMB temperature maps from Planck

TL;DR

This study investigates residual foreground contamination in Planck's cleaned CMB maps outside the galactic mask by cross-correlating with galactic emission templates, leading to an improved mask for cleaner CMB analysis.

Contribution

The paper introduces a method to identify residual foregrounds in cleaned CMB maps and proposes an enhanced mask to improve the reliability of cosmological inferences.

Findings

Few regions outside the galactic mask are contaminated.

A new mask is derived to exclude residual foregrounds.

The method improves the reliability of CMB analyses.

Abstract

Maps of cosmic microwave background (CMB) are extracted from multi-frequency observations using a variety of cleaning procedures. However, in regions of strong microwave emission, particularly in the galactic plane from our own galaxy Milky Way and some extended or point sources, the recovered CMB signal is not reliable. Thus, a galactic mask is provided along with the \emph{cleaned} CMB sky for use with that CMB map which excises sky regions that may still be potentially contaminated even after cleaning. So, to avoid bias in our inferences, we impose such a foreground mask. In this paper, we analyze a cleaned CMB map from Planck PR4 to probe for any foreground residuals that may still be present \emph{outside} the galactic mask where the derived CMB sky is considered clean. To that end, we employ a local cross-correlation coefficient statistic where we cross-correlate widely used foreground templates that trace galactic synchrotron, free-free, and thermal dust emission from our galaxy with the cleaned CMB sky. Using simulations, we find that few regions of the derived CMB sky are still contaminated and have to be omitted. Based on this study, we derived a mask that could be used in conjugation with the standard mask to further improve the purpose of galactic masks.