Statistical properties of galactic CMB foregrounds: dust and synchrotron

TL;DR

This paper analyzes the statistical properties of galactic dust and synchrotron foregrounds in the CMB, focusing on polarization modes and cross-correlations, using MHD turbulence models to interpret Planck data.

Contribution

It extends previous work on dust polarization by including TE cross-correlation and develops a formalism for synchrotron, linking these properties to galactic turbulence characteristics.

Findings

Planck data consistent with sub-Alfvénic turbulence

B/E ratio and TE cross-correlation inform on galactic magnetization

Turbulence properties influence polarization statistics

Abstract

Recent Planck observations have revealed some of the important statistical properties of synchrotron and dust polarisation, namely, the $B$ to $E$ mode power and temperature-$E$ (TE) mode cross-correlation. In this paper, we extend our analysis in Kandel et al. (2017) that studied $B$ to $E$ mode power ratio for polarised dust emission to include TE cross-correlation and develop an analogous formalism for synchrotron signal, all using a realistic model of magnetohydrodynamical (MHD) turbulence. Our results suggest that the Planck results for both synchrotron and dust polarisation can be understood if the turbulence in the Galaxy is sufficiently sub-Alfv\'enic. We also show how $B$ to $E$ ratio as well as the TE cross-correlation can be used to study media magnetisation, compressibility, and level of density-magnetic field correlation.