Polarized Foreground Emission from Dust: Grain Alignment and MHD Turbulence

TL;DR

This paper reviews the physical processes behind dust grain alignment in the interstellar medium, highlighting the radiative torque mechanism as a promising explanation for polarized foreground emission affecting cosmic microwave background studies.

Contribution

It provides a comprehensive review of grain alignment mechanisms, emphasizing the renewed interest in radiative torque alignment over traditional theories.

Findings

Radiative torque mechanism is now considered the most promising for grain alignment.

Alignment of small grains explains anomalous foreground emission in 10-90 GHz range.

Magnetic grains contribute to polarization signals in the interstellar medium.

Abstract

Aligned grains present a foreground for cosmic microwave emission studies. We review basic physical processes involved in grain alignment and discuss the niches for different alignment mechanisms. We show that mechanisms which were favored for decades do not look so promising right now, while the radiative torque mechanism ignored for more than 20 years looks quite attractive. We discuss alignment of small rotating grains that are thought to be responsible for 10-90 GHz anomalous foreground and polarization arising from magnetic grains.