Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC6334I
Abstract
Intense radiation from high-mass stars is expected to significantly affect dust grain alignment and evolution through RAdiative Torques (RATs). We investigate this effect in a massive star-forming region, NGC6334I, using 1.2 mm dust continuum polarization observations from the Atacama Large Millimeter/submillimeter Array. The polarization fraction spans from ≲1% to ∼10% and decreases with increasing column density, remaining below 2% in dense cores despite high temperatures (∼100 K), where efficient grain alignment by RATs is expected. We investigate how grain alignment, grain growth, grain disruption, B-field tangling, and local physical conditions affect the polarization properties of MM1, MM2, MM3, and their surroundings. Polarization angle dispersion shows that B-field tangling contributes to depolarization at moderate densities but cannot fully explain the lowest polarization fractions. Using RAT-based grain alignment and polarization modeling, we find that reduced alignment efficiency and high optical depth reproduce the low polarization in the densest regions. MM2 shows evidence of grain growth, with maximum grain sizes amax∼0.35−1.0 μm, while MM1 exhibits smaller values of ∼0.35−0.50 μm. Accounting for optical depth increases the inferred grain sizes in MM1 to ∼1.0−2.0 μm. Analytical estimates of radiative torque disruption from the intense outburst suggest that micron-sized grains in high-temperature, moderate-density regions can fragment into submicron grains. Alternatively, high optical depth may also explain the low polarization in the densest regions even in the presence of micron-sized grains. Incorporating the B-field inclination effect indicates a transition from predominantly plane-of-sky fields at low densities to more line-of-sight-aligned configurations at high densities.
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BibTeX
@misc{rawat2026magnetic,
title = {{Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC6334I}},
author = {Vineet Rawat and Thiem Hoang and Patricio Sanhueza and Ian W. Stephens and Manuel Fernández López and Paulo Cortés and Jihye Hwang and Junhao Liu and Kaho Morii and Josep Miquel Girart and Ji-Hyun Kang and Yu Cheng and Shanghuo Li and Luis A. Zapata and Eun Jung Chung and Fernando A. Olguin and Huei-Ru Vivien Chen and Piyali Saha and Chakali Eswaraiah and Qizhou Zhang and O. R. Jadhav},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.03458},
eprint = {2609.03458},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.03458},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC6334I
AU - Vineet Rawat
AU - Thiem Hoang
AU - Patricio Sanhueza
AU - Ian W. Stephens
AU - Manuel Fernández López
AU - Paulo Cortés
AU - Jihye Hwang
AU - Junhao Liu
AU - Kaho Morii
AU - Josep Miquel Girart
AU - Ji-Hyun Kang
AU - Yu Cheng
AU - Shanghuo Li
AU - Luis A. Zapata
AU - Eun Jung Chung
AU - Fernando A. Olguin
AU - Huei-Ru Vivien Chen
AU - Piyali Saha
AU - Chakali Eswaraiah
AU - Qizhou Zhang
AU - O. R. Jadhav
PY - 2026
DA - 2026/09/06
PB - arXiv
DO - 10.48550/arxiv.2609.03458
UR - https://arxiv.org/abs/2609.03458
AB - Intense radiation from high-mass stars is expected to significantly affect dust grain alignment and evolution through RAdiative Torques (RATs). We investigate this effect in a massive star-forming region, NGC6334I, using 1.2 mm dust continuum polarization observations from the Atacama Large Millimeter/submillimeter Array. The polarization fraction spans from ≲1% to ∼10% and decreases with increasing column density, remaining below 2% in dense cores despite high temperatures (∼100 K), where efficient grain alignment by RATs is expected. We investigate how grain alignment, grain growth, grain disruption, B-field tangling, and local physical conditions affect the polarization properties of MM1, MM2, MM3, and their surroundings. Polarization angle dispersion shows that B-field tangling contributes to depolarization at moderate densities but cannot fully explain the lowest polarization fractions. Using RAT-based grain alignment and polarization modeling, we find that reduced alignment efficiency and high optical depth reproduce the low polarization in the densest regions. MM2 shows evidence of grain growth, with maximum grain sizes a_max∼0.35−1.0 μm, while MM1 exhibits smaller values of ∼0.35−0.50 μm. Accounting for optical depth increases the inferred grain sizes in MM1 to ∼1.0−2.0 μm. Analytical estimates of radiative torque disruption from the intense outburst suggest that micron-sized grains in high-temperature, moderate-density regions can fragment into submicron grains. Alternatively, high optical depth may also explain the low polarization in the densest regions even in the presence of micron-sized grains. Incorporating the B-field inclination effect indicates a transition from predominantly plane-of-sky fields at low densities to more line-of-sight-aligned configurations at high densities.
ER -