The JCMT BISTRO-2 Survey: The Magnetic Field in the Center of the Rosette Molecular Cloud
Pattle, Kate; Karoly, Janik; Ward-Thompson, Derek; Berry, David; Bastien, Pierre; Ching, Tao-Chung; Coudé, Simon; Hwang, Jihye; Kwon, Woojin; Soam, Archana; Wang, Jia-Wei; Hasegawa, Tetsuo; Lai, Shih-Ping; Qiu, Keping; Arzoumanian, Doris; Chen, Zhiwei; Di Francesco, James; Diep, Pham Ngoc; Eswaraiah, Chakali; Fanciullo, Lapo; Hoang, Thiem; Hull, Charles L. H.; Johnstone, Doug; Könyves, Vera; Kang, Ji-hyun; Kirchschlager, Florian; Koch, Patrick M.; Kwon, Jungmi; Lee, Chang Won; Onaka, Takashi; Tahani, Mehrnoosh; Tamura, Motohide; Tang, Xindi; Robitaille, Jean-François; Furuya, Ray S.; Kirk, Jason M.
United Kingdom, Ireland, Canada, France, China, Vietnam, Taiwan, Japan, South Korea, United States, Chile
Abstract
We present the first 850 μm polarization observations in the most active star-forming site of the Rosette Molecular Cloud (d ∼ 1.6 kpc) in the wall of the Rosette Nebula, imaged with the SCUBA-2/POL-2 instruments of the James Clerk Maxwell telescope, as part of the B-Fields In Star-forming Region Observations 2 (BISTRO-2) survey. From the POL-2 data we find that the polarization fraction decreases with the 850 μm continuum intensity with α = 0.49 ± 0.08 in the p ∝ I-α relation, which suggests that some fraction of the dust grains remain aligned at high densities. The north of our 850 μm image reveals a "gemstone ring" morphology, which is a ∼1 pc diameter ring-like structure with extended emission in the "head" to the southwest. We hypothesize that it might have been blown by feedback in its interior, while the B-field is parallel to its circumference in most places. In the south of our SCUBA-2 field the clumps are apparently connected with filaments that follow infrared dark clouds. Here, the POL-2 magnetic field orientations appear bimodal with respect to the large-scale Planck field. The mass of our effective mapped area is ∼174 M⊙, which we calculate from 850 μm flux densities. We compare our results with masses from large-scale emission-subtracted Herschel 250 μm data and find agreement within 30%. We estimate the plane-of-sky B-field strength in one typical subregion using the Davis-Chandrasekhar-Fermi technique and find 80 ± 30 μG toward a clump and its outskirts. The estimated mass-to-flux ratio of λ = 2.3 ± 1.0 suggests that the B-field is not sufficiently strong to prevent gravitational collapse in this subregion.