Kavli Affiliate: Ke Wang
| First 5 Authors: Junhao Liu, Qizhou Zhang, Yuxin Lin, Keping Qiu, Patrick M. Koch
| Summary:
We have comprehensively studied the multi-scale physical properties of the
infrared dark cloud (IRDC) G28.34 (the Dragon cloud) with dust polarization and
molecular line data from Planck, FCRAO-14m, JCMT, and ALMA. We find that the
averaged magnetic fields of clumps tend to be either parallel with or
perpendicular to the cloud-scale magnetic fields, while the cores in clump MM4
tend to have magnetic fields aligned with the clump fields. Implementing the
relative orientation analysis (for magnetic fields, column density gradients,
and local gravity), Velocity Gradient Technique, and modified
Davis-Chandrasekhar-Fermi analysis, we find that: G28.34 is located in a
trans-to-sub-Alfv'{e}nic environment ($mathcal{M}_{A}=0.74$ within $r=15$
pc); the magnetic field is effectively resisting gravitational collapse in
large-scale diffuse gas, but is distorted by gravity within the cloud and
affected by star formation activities in high-density regions; and the
normalized mass-to-flux ratio tends to increase with density and decrease with
radius. Considering both the magnetic and turbulent support, we find that the
environmental gas of G28.34 is in a super-virial (supported) state, the
infrared dark clumps may be in a near-equilibrium state, and core MM4-core4 is
in a sub-virial (gravity-dominant) state. In summary, we suggest that magnetic
fields dominate gravity and turbulence in the cloud environment at large
scales, resulting in relatively slow cloud formation and evolution processes.
Within the cloud, gravity could overwhelm both magnetic fields and turbulence,
allowing local dynamical star formation to happen.
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