Quantitative Polarimetry: A Unified Model of Dust Grain Alignment by Magnetic Radiative Torques

Abstract: Polarization of optical starlight and far-infrared thermal dust emission due to alignment of interstellar grains offers a powerful window to study magnetic fields in the various astrophysical environments, from the diffuse interstellar medium to accretion disks surrounding young stars. Precision cosmology requires accurate model of Galactic dust polarization for the first detection of Cosmic Microwave Background (CMB) B-modes signal. Such an accurate model is only achieved when a quantitative theory of grain alignment that links grain alignment efficiency with local physical conditions and dust properties is developed and tested. In this paper, we review the successful development of such a quantitative alignment theory, focusing on a unified model of grain alignment based on radiative torques and magnetic relaxation for dust grains incorporated with iron inclusions. We discuss the implication of the unified alignment model for interpreting the latest observational results by Planck and ALMA.