B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). I. The Massive Filament G11.11–0.12 Observed by SOFIA/HAWC+

Abstract

We report the first measurement of polarized thermal dust emission toward the entire infrared dark cloud G11.11−0.12 taken by the polarimeter SOFIA/HAWC+ at 214 μm. The obtained magnetic fields (B-fields) from the polarized emission of the early-stage and massive filament tend to be perpendicular to its spine. We produce a map of B-field strengths for the center region of the filament. The strengths vary in the range of 100–600 μG and are strongest along the filament's spine. The central region is sub-Alfvénic and mostly subcritical, meaning that B-fields dominate over turbulence and are strong enough to resist gravitational collapse. The alignment and properties of dust grains in the filament are studied using radiative torque (RAT) theory. We find the decrease of polarization degree P with emission intensity I, i.e., depolarization effect, of the form P ∝ I −α with α ∼ 0.8–0.9, implying a significant loss of grain alignment in the filament's spine. The depolarization can be explained by the decrease in RAT alignment efficiency toward the denser regions with weaker radiation field, which cannot be explained by B-field tangling. We study the effect of the enhanced magnetic relaxation by embedded iron inclusions on RAT alignment and find that the high polarization fraction P ∼ 20%–30% in the outer layer of the filament is potential evidence for the magnetically enhanced RAT alignment mechanism. This is the first time this effect is evaluated in a filament. Based on the polarization fraction and RAT alignment theory, we also find evidence for grain growth in the filament.

Evidence of Grain Alignment by Magnetically Enhanced Radiative Torques from Multiwavelength Dust Polarization Modeling of HL Tau

“…Under the framework of MRAT, grains can efficiently be aligned with magnetic fields owing to the enhanced efficiency by RATs and (super)paramagnetic relaxation due to iron inclusion within the grains Hoang & Lazarian 2016). Recent observations show more evidence for iron inclusion in the form of clusters in different environments, such as in the protostellar core (Giang et al 2023), filament (Ngoc et al 2023), and the envelope of evolved stars (Truong et al 2023). RATs can spin grains up to suprathermal rotation (so-called high-J attractors) or de-spin them down to thermal rotation (so-called low-J attractors).…”

Polarized Light from Massive Protoclusters (POLIMAP). I. Dissecting the Role of Magnetic Fields in the Massive Infrared Dark Cloud G28.37+0.07

“…A correlation between magnetic field morphology and filament density structure indicating perpendicular alignment with filament orientations has been reported (e.g., Liu et al 2018;Soam et al 2019). However, these studies have concerned only a handful of IRDCs, e.g., G11.11-0.12 (the "Snake"), G34.34+0.24, G35.39-0.33, and the "Brick" (Pillai et al 2015;Hoq et al 2017;Liu et al 2018;Soam et al 2019;Tang et al 2019;Vahdanian & Nejad-Asghar 2022;Chen et al 2023;Ngoc et al 2023;Xu et al 2023a;Gu et al 2024). Hence, a systematic study of IRDCs that span a range of masses, sizes, and environments is an important next step further to understanding the links between the magnetic field and IRDC properties, and thus to better constrain the initial conditions of massive star and star cluster formation.…”

Probing 3D Magnetic Fields Using Thermal Dust Polarization and Grain Alignment Theory

“…Moreover, the disregarding of the B-field fluctuations along the LOS in Chen et al (2019) is only valid for the case of a strongly magnetized medium (i.e., sub-Alfvén turbulence, M A = δv/v A = δB/B < 1), where δv = v l for the turbulence velocity. However, polarimetric observations toward molecular clouds and dense clouds/cores reveal that the Alfvén turbulence is usually sub-Alfvénic, Pattle et al 2021;Karoly et al 2023;Ngoc et al 2023;. However, the turbulence becomes super-Alfvénic with M A > 1 in high-density regions of n H > 10 7 cm −3 (see Figure 2(f) in Pattle et al 2023).…”