Polarization of FIR emission from T Tauri Disks

TL;DR

This paper investigates dust grain alignment and polarization in T Tauri disks, demonstrating how magnetic field structures can be inferred from sub-mm/FIR polarization observations and modeling.

Contribution

It presents a detailed analysis of dust grain alignment efficiency and polarization predictions in T Tauri disks, linking polarization degree to disk properties and magnetic fields.

Findings

Dust grains farther from the star are more efficiently aligned.

Polarization degree is around 2-3% at wavelengths >100 μm.

Polarization direction is perpendicular to magnetic field lines.

Abstract

Recent observation of 850 micron sub-mm polarization from T Tauri disks opens up the possibility of studying magnetic field structure within protostellar disks. The degree of polarization is around 3 % and the direction of polarization is perpendicular to the disk. Since thermal emission from dust grains dominates the spectral energy distribution at the sub-mm/FIR regime, dust grains are thought to be the cause of the polarization. We discuss grain alignment by radiation and we explore the efficiency of dust alignment in T Tauri disks. Calculations show that dust grains located far away from the Central proto-star are more efficiently aligned. In the presence of a regular magnetic field, the aligned grains produce polarized emission in sub-mm/FIR wavelengths. The direction of polarization is perpendicular to the local magnetic field direction. When we use a recent T Tauri disk model and take a Mathis-Rumpl-Nordsieck-type distribution with maximum grain size of 500-1000 $\mu$m, the degree of polarization is around 2-3 % level at wavelengths larger than $\sim100\mu$m. Our study indicates that multifrequency infrared polarimetric studies of protostellar disks can provide good insights into the details of their magnetic structure. We also provide predictions for polarized emission for disks viewed at different wavelengths and viewing angles.