High circular polarization of near infrared light induced by micron-size dust grains

TL;DR

This study demonstrates that micron-sized dust grains in star-forming regions can produce high degrees of circular polarization in near-infrared light, explaining observed polarization patterns.

Contribution

It introduces three-dimensional radiative transfer simulations showing how dust grain size and configuration affect circular polarization in star-forming regions.

Findings

CP degree exceeds 20% for micron-sized grains

CP distribution shows asymmetric quadrupole patterns

CP can reach up to 60% depending on dust slab position

Abstract

We explore the induction of circular polarization (CP) of near-infrared light in star-forming regions using three-dimensional radiative transfer calculations. The simulations trace the change of Stokes parameters at each scattering/absorption process in a dusty gas slab composed of aligned grains. We find that the CP degree enlarges significantly according as the size of dust grains increases and exceeds $\sim 20$ percent for micron-size grains. Therefore, if micron-size grains are dominant in a dusty gas slab, the high CP observed around luminous young stellar objects can be accounted for. The distributions of CP show the asymmetric quadrupole patters regardless of the grain sizes. Also, we find that the CP degree depends on the relative position of a dusty gas slab. If a dusty gas slab is located behind a star-forming region, the CP reaches $\sim 60$ percent in the case of $1.0~{\rm \mu m}$ dust grains. Hence, we suggest that the observed variety of CP maps can be explained by different size distributions of dust grains and the configuration of aligned grains.