Interstellar polarization and the alignment of interstellar dust grains

Interstellar dust grains aligned in magnetic fields induce the polarization of starlight by differential extinction, and their polarized thermal emission contaminates with polarized cosmic microwave background (CMB) signal. Studying dust polarization not only is important for understanding magnetic fields, star formation, dust composition, but also for CMB polarization missions. 

However, the question why dust grains get aligned with magnetic fields has been challenged for more than sixty years. In this talk, I shall present a predictive model of grain alignment based on radiative torques (RATs) arising from anisotropic radiation acting on helical grains. 

I shall begin with a simple analytical model that can reproduce generic properties of radiative torques obtained for irregular shapes using Discrete Dipole Approximation code. I then discuss fundamental and testable properties of the RAT alignment and the alignment in the presence of additional torques. I shall present an algorithm for modeling dust polarization by aligned grains due to RATs and RATs plus H2 formation torques, and compare obtained results with observations. 

Good agreement of the theoretical predictions with observational data for various environment conditions indicates that the RAT alignment can be a dominant mechanism of grain alignment. If time permits, I will talk about the polarization of spinning dust emission and alignment of polycyclic aromatic hydrocarbons.