Detectability of Galactic Faraday Rotation in Multi-wavelength CMB Observations: A Cross-Correlation Analysis of CMB and Radio Maps

TL;DR

This paper presents a novel cross-correlation method to detect galactic Faraday Rotation in CMB data, significantly enhancing sensitivity over previous single-frequency estimators and enabling high-confidence detections with upcoming experiments.

Contribution

The authors develop a new cross-correlation technique that improves Faraday Rotation detection sensitivity in CMB observations by a factor of about 30 compared to traditional methods.

Findings

A factor of ~30 increase in sensitivity over single-frequency estimators.

Predicted >10σ detection significance for CMB-S4-like experiments.

Enhanced detection prospects with future radio polarization surveys.

Abstract

We introduce a new cross-correlation method to detect and verify the astrophysical origin of Faraday Rotation (FR) in multiwavelength surveys. FR is well studied in radio astronomy from radio point sources but the $\lambda^{2}$ suppression of FR makes detecting and accounting for this effect difficult at millimeter and sub-millimeter wavelengths. Therefore statistical methods are used to attempt to detect FR in the cosmic microwave background (CMB). Most estimators of the FR power spectrum rely on single frequency data. In contrast, we investigate the correlation of polarized CMB maps with FR measure maps from radio point sources. We show a factor of $\sim30$ increase in sensitivity over single frequency estimators and predict detections exceeding $10\sigma$ significance for a CMB-S4 like experiment. Improvements in observations of FR from current and future radio polarization surveys will greatly increase the usefulness of this method.