Constraint on the Polarization of Electric Dipole Emission from Spinning Dust

TL;DR

This study constrains the polarization levels of electric dipole emission from spinning dust, particularly PAHs, and assesses their potential contamination of polarized CMB measurements.

Contribution

It provides the first detailed polarization constraints on spinning dust emission based on specific star polarization features and grain alignment models.

Findings

Polarization of spinning dust emission is about 1.6% at 3 GHz.

Polarization drops below 0.9% above 20 GHz.

Thermal dust polarization is predicted to be around 11-14% at 353 GHz.

Abstract

Planck results have revealed that the electric dipole emission from polycyclic aromatic hydrocarbons (PAHs) is the most reliable explanation for anomalous microwave emission that interferes with cosmic microwave background (CMB) radiation experiments. The emerging question is to what extent this emission component contaminates to the polarized CMB radiation. We present constraints on polarized dust emission for the model of grain size distribution and grain alignment that best fits to observed extinction and polarization curves. Two stars with a prominent polarization feature at wavelength 2175 Angstrom, HD 197770 and HD 147933-4, are chosen for our study. For HD 197770, we find that the model with aligned silicate grains plus weakly aligned PAHs can successfully reproduce the 2175 Angstrom polarization feature; whereas, for HD 147933-4, we find that the alignment of only silicate grains can account for that feature. The alignment function of PAHs for the best-fit model to the HD 197770 data is employed to constrain polarized spinning dust emission. We find that the degree of polarization of spinning dust emission is about 1.6 percent at frequency ~ 3 GHz and declines to below 0.9 percent for frequency above 20 GHz. We also predict the degree of polarization of thermal dust emission at 353 GHz to be ~ 11 percent and 14 percent for the lines of sight to the HD 197770 and HD 147933-4 stars, respectively.