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Peer-reviewedCC BY 4.0The Astrophysical Journal

Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC 6334I

  • Vineet Rawat1
  • Thiem Hoang1,2
  • Patricio Sanhueza3
  • Ian W. Stephens4
  • Manuel Fernández López5
  • Paulo Cortés6,7
  • Jihye Hwang8
  • Junhao Liu9,10
  • Kaho Morii11
  • Josep Miquel Girart5,12
  • Ji-hyun Kang1
  • Yu Cheng13
9 more authors
  • Shanghuo Li9
  • Luis A. Zapata14
  • Eun Jung Chung1
  • Fernando A. Olguin13,15
  • Huei-Ru Vivien Chen16
  • Piyali Saha17
  • Eswaraiah Chakali18
  • Qizhou Zhang11
  • O. R. Jadhav19,20
20 affiliations
  1. 1Korea Astronomy and Space Science Institute (KASI)
  2. 2Korea University of Science and Technology
  3. 3The University of Tokyo
  4. 4Worcester State University
  5. 5Institut de Ciències de l’Espai (ICE-CSIC)
  6. 6Joint ALMA Observatory
  7. 7National Radio Astronomy Observatory
  8. 8Kyushu University
  9. 9Nanjing University
  10. 10Key Laboratory of Modern Astronomy and Astrophysics (Nanjing University)
  11. 11Center for Astrophysics ∣ Harvard & Smithsonian
  12. 12Institut d’Estudis Espacials de Catalunya (IEEC)
  13. 13National Astronomical Observatory of Japan
  14. 14Universidad Nacional Autónoma de México
  15. 15Kyoto University
  16. 16National Tsing Hua University
  17. 17Academia Sinica Institute of Astronomy and Astrophysics
  18. 18Indian Institute of Science Education and Research (IISER) Mohali
  19. 19Astronomy & Astrophysics Division
  20. 20Indian Institute of Technology Gandhinagar Palaj
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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, NGC 6334I, 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 μ m, while MM1 exhibits smaller values of ∼0.35–0.50 μ m. Accounting for optical depth increases the inferred grain sizes in MM1 to ∼1.0–2.0 μ m. Analytical estimates of RAT 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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Cite

BibTeXRIS
BibTeX
@article{rawat2026magnetic,
  title = {{Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC 6334I}},
  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 Eswaraiah Chakali and Qizhou Zhang and O. R. Jadhav},
  journal = {The Astrophysical Journal},
  year = {2026},
  month = nov,
  doi = {10.3847/1538-4357/aea3f6},
  url = {https://iopscience.iop.org/article/10.3847/1538-4357/aea3f6},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Magnetic Fields in Massive Star-forming Regions (MagMaR). IX. Radiative Torque Alignment and Disruption in NGC 6334I
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  - Eswaraiah Chakali
AU  - Qizhou Zhang
AU  - O. R. Jadhav
PY  - 2026
DA  - 2026/11/05
JO  - The Astrophysical Journal
DO  - 10.3847/1538-4357/aea3f6
UR  - https://iopscience.iop.org/article/10.3847/1538-4357/aea3f6
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, NGC 6334I, 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 μ m, while MM1 exhibits smaller values of ∼0.35–0.50 μ m. Accounting for optical depth increases the inferred grain sizes in MM1 to ∼1.0–2.0 μ m. Analytical estimates of RAT 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.
SN  - 1538-4357
SN  - 0004-637X
ER  -