| 1. |
- Ching, Tao-Chung, et al.
(författare)
-
The JCMT BISTRO-2 Survey: Magnetic Fields of the Massive DR21 Filament
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 941:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present 850 mu m dust polarization observations of the massive DR21 filament from the B-fields In STar-forming Region Observations (BISTRO) survey, using the POL-2 polarimeter and the SCUBA-2 camera on the James Clerk Maxwell Telescope. We detect ordered magnetic fields perpendicular to the parsec-scale ridge of the DR21 main filament. In the subfilaments, the magnetic fields are mainly parallel to the filamentary structures and smoothly connect to the magnetic fields of the main filament. We compare the POL-2 and Planck dust polarization observations to study the magnetic field structures of the DR21 filament on 0.1-10 pc scales. The magnetic fields revealed in the Planck data are well-aligned with those of the POL-2 data, indicating a smooth variation of magnetic fields from large to small scales. The plane-of-sky magnetic field strengths derived from angular dispersion functions of dust polarization are 0.6-1.0 mG in the DR21 filament and similar to 0.1 mG in the surrounding ambient gas. The mass-to-flux ratios are found to be magnetically supercritical in the filament and slightly subcritical to nearly critical in the ambient gas. The alignment between column density structures and magnetic fields changes from random alignment in the low-density ambient gas probed by Planck to mostly perpendicular in the high-density main filament probed by James Clerk Maxwell Telescope. The magnetic field structures of the DR21 filament are in agreement with MHD simulations of a strongly magnetized medium, suggesting that magnetic fields play an important role in shaping the DR21 main filament and subfilaments.
|
|
| 2. |
- Shimajiri, Y., et al.
(författare)
-
Probing accretion of ambient cloud material into the Taurus B211/B213 filament
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 623
-
Tidskriftsartikel (refereegranskat)abstract
- Context. Herschel observations have emphasized the role of molecular filaments in star formation. However, the origin and evolution of these filaments are not yet well understood, partly because of the lack of kinematic information. Aims. We confirm from a kinematic viewpoint that the Taurus B211/B213 filament is accreting background cloud material, and we investigate the potential influence of large-scale external effects on the formation of the filament. Methods. To examine whether the B211/B213 filament is accreting background gas because of its gravitational potential, we produced a toy accretion model and compared its predictions to the velocity patterns observed in (CO)-C-12 (1-0) and (CO)-C-13 (1-0). We also examined the spatial distributions of H alpha, Planck 857 GHz dust continuum, and HI emission to search for evidence of large-scale external effects. Results. We estimate that the depth of the Taurus cloud around the B211/B213 filament is similar to 0.3-0.7 pc under the assumption that the density of the gas is the same as the critical density of (CO)-C-13 (1-0). Compared to a linear extent of >10 pc in the plane of the sky, this suggests that the 3D morphology of the cloud surrounding the B211/B213 filament is sheet-like. Position-velocity (PV) diagrams observed in (CO)-C-12 (1-0) and (CO)-C-13 (1-0) perpendicular to the filament axis show that the emission from the gas surrounding B211/B213 is redshifted to the northeast of the filament and blueshifted to the southwest, and that the velocities of both components approach the velocity of the B211/B213 filament as the line of sight approaches the crest of the filament. The PV diagrams predicted by our accretion model are in good agreement with the observed (CO)-C-12 (1-0) and (CO)-C-13 (1-0) PV diagrams, supporting the previously proposed scenario of mass accretion into the filament. Moreover, inspection of the spatial distribution of the H alpha and Planck 857 GHz emission in the Taurus-California-Perseus region on scales up to >200 pc suggests that the B211/B213 filament may have formed as a result of an expanding supershell generated by the Per OB2 association. Conclusions. Based on these results, we propose a scenario in which the B211/B213 filament was initially formed by large-scale compression of HI gas and is now growing in mass by gravitationally accreting molecular gas of the ambient cloud.
|
|
