Investigation of Hourglass-shaped Magnetic Fields in the G35.20–0.74 Star-forming Complex

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Abstract
To investigate the role of magnetic fields toward the G35N and G35S subregions in the G35.20–0.74 star-forming complex, we utilized multiwavelength polarimetric observations from the SOFIA/HAWC+ at 154 μ m and Atacama Cosmology Telescope (ACT) at 220 GHz/1.3 mm. The ACT 220 GHz polarization data (resolution ∼1 ′ ) show an hourglass-shaped plane-of-sky magnetic field morphologies toward both the subregions, though with distinct symmetry axes. SOFIA/HAWC+ 154 μ m data (resolution ∼13 . ″ 6) confirm an hourglass morphology in G35N, whereas G35S displays a different magnetic field configuration compared to the ACT observations. An hourglass morphology identified at clump scales (∼a parsec) toward G35N is consistent with the previously reported B -field morphology at core scales (∼0.05 pc), supporting the scenario of a magnetically regulated collapse. Using the SOFIA/HAWC+ data, we estimate magnetic field strengths of ∼600 ± 200 μ G in G35N and ∼850 ± 310 μ G in G35S. Energy balance analysis suggests that gravity and magnetic fields contribute comparably in G35N, while in G35S the gas dynamics are dominated by magnetic field, followed by gravity and turbulence. The higher field strength in G35S likely results from compression by the expanding H ii region, highlighting the impact of stellar feedback. The derived magnetic field strengths and corresponding magnetic energies should be treated as upper limits due to unresolved beam-scale correlations and the limited fitting range of the polarization angle structure function. Overall, our results show that magnetic fields decisively regulate star formation, with G35N shaped by magnetically controlled collapse and G35S being strongly influenced by stellar feedback.

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