Faraday Rotation as a diagnostic of Galactic foreground contamination of CMB maps

TL;DR

This study investigates the potential impact of galactic foreground contamination, specifically from outside the galactic plane, on CMB temperature maps using Faraday rotation correlations, revealing significant associations and possible explanations for anomalies like the Cold Spot.

Contribution

It introduces an analysis of extragalactic foreground contamination in CMB maps through Faraday rotation, highlighting correlations outside the galactic plane and implications for CMB anomalies.

Findings

Significant deviation of cross-correlation from simulations at 99.9% level.

Overlap between CMB temperature extrema and Faraday rotation extrema.

Correlation between Faraday rotation and CMB temperature near galactic radio loops.

Abstract

The contribution from the residuals of the foreground can have a significant impact on the temperature maps of the Cosmic Microwave Background (CMB). Mostly, the focus has been on the galactic plane, when foreground cleaning has taken place. However, in this paper, we will investigate the possible foreground contamination, from sources outside the galactic plane in the CMB maps. We will analyze the correlation between the Faraday rotation map and the CMB temperature map. The Faraday rotation map is dependent on the galactic magnetic field, as well as the thermal electron density, and both may contribute to the CMB temperature. We find that the standard deviation for the mean cross correlation deviate from that of simulations at the 99.9% level. Additionally, a comparison between the CMB temperature extrema and the extremum points of the Faraday rotation is also performed, showing a general overlap between the two. Also we find that the CMB Cold Spot is located at an area of strong negative cross correlation, meaning that it may be explained by a galactic origin. Further, we investigate nearby supernova remnants in the galaxy, traced by the galactic radio loops. These super nova remnants are located at high and low galactic latitude, and thus well outside the galactic plane. We find some correlation between the Faraday Rotation and the CMB temperature, at select radio loops. This indicate, that the galactic foregrounds may affect the CMB, at high galactic latitudes