2018ApJ...859..151L

Magnetic field plays a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained owing to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 µm with SCUBA-2/POL-2 at JCMT for the first time. The magnetic field tends to be perpendicular to the densest part of the main filament (F_M), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of ∼50 µG for F_M is obtained using the Davis-Chandrasekhar-Fermi method. Based on ¹³CO (1-0) line observations, we suggest a formation scenario of F_M due to large-scale (∼10 pc) cloud-cloud collision. Using additional NH₃ line data, we estimate that F_M will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F_M, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F_M are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F_M may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive (∼200 M_☉), collapsing starless clump candidate, "c8," in G035.39-00.33. The magnetic field surrounding "c8" is likely pinched, hinting at an accretion flow along the filament.