Polarized galactic synchrotron and dust emission and their correlation

TL;DR

This study analyzes polarized dust and synchrotron emissions using WMAP9 and Planck data to assess foreground contamination in CMB measurements, revealing spatial correlations and modeling their impact on cosmological observations.

Contribution

It provides the first detailed analysis of polarized dust and synchrotron correlation using WMAP and Planck data, informing foreground modeling for CMB studies.

Findings

Spatial correlation between dust and synchrotron emission with rho≈0.4 for low multipoles.

A simple model fits all cross spectra within current uncertainties.

In the cleanest sky regions, synchrotron amplitude is about 30% of dust at 90 GHz for certain multipoles.

Abstract

We present an analysis of the level of polarized dust and synchrotron emission using the WMAP9 and Planck data. The primary goal of this study is to inform the assessment of foreground contamination in the cosmic microwave background (CMB) measurements below $\ell\sim200$ from 23 to 353 GHz. We compute angular power spectra as a function of sky cut based on the Planck 353 GHz polarization maps. Our primary findings are the following. (1) There is a spatial correlation between the dust emission as measured by Planck at 353 GHz and the synchrotron emission as measured by WMAP at 23 GHz with $\rho\approx0.4$ or greater for $\ell<20$ and $f_{\mathrm{sky}}\geq0.5$, dropping to $\rho\approx0.2$ for $30<\ell<200$. (2) A simple foreground model with dust, synchrotron, and their correlation fits well to all possible cross spectra formed with the WMAP and Planck 353 GHz data given the current uncertainties. (3) In the 50$\%$ cleanest region of the polarized dust map, the ratio of synchrotron to dust amplitudes at 90 GHz for 50 $\leq \ell \leq$110 is $0.3_{-0.2}^{+0.3}$. Smaller regions of sky can be cleaner although the uncertainties in our knowledge of synchrotron emission are larger. A high-sensitivity measurement of synchrotron below 90 GHz will be important for understanding all the components of foreground emission near 90 GHz.