Multi-scale physical properties of NGC 6334 as revealed by relative orientations between magnetic fields, density gradients, velocity gradients, and gravity

Junhao Liu, Qizhou Zhang, Patrick M. Koch, Hauyu Baobab Liu, Zhi-Yun Li, Shanghuo Li, Josep Miquel Girart, Huei-Ru Vivien Chen, Tao-Chung Ching, Paul Ho, Shih-Ping Lai, Keping Qiu, Ramprasad Rao, Ya-wen Tang

Submitted on 31 October 2022


We present ALMA dust polarization and molecular line observations toward 4 clumps (I(N), I, IV, and V) in the massive star-forming region NGC 6334. In conjunction with large-scale dust polarization and molecular line data from JCMT, Planck, and NANTEN2, we make a synergistic analysis of relative orientations between magnetic fields (θB), column density gradients (θNG), local gravity (θLG), and velocity gradients (θVG) to investigate the multi-scale (from 30 pc to 0.003 pc) physical properties in NGC 6334. We find that the relative orientation between θB and θNG changes from statistically more perpendicular to parallel as column density (NH2) increases, which is a signature of trans-to-sub-Alfv\'{e}nic turbulence at complex/cloud scales as revealed by previous numerical studies. Because θNG and θLG are preferentially aligned within the NGC 6334 cloud, we suggest that the more parallel alignment between θB and θNG at higher NH2 is because the magnetic field line is dragged by gravity. At even higher NH2, the angle between θB and θNG or θLG transits back to having no preferred orientation or statistically slightly more perpendicular, suggesting that the magnetic field structure is impacted by star formation activities. A statistically more perpendicular alignment is found between θB and θVG throughout our studied NH2 range, which indicates a trans-to-sub-Alfv\'{e}nic state at small scales as well. The normalised mass-to-flux ratio derived from the polarization-intensity gradient (KTH) method increases with NH2.


Comment: 27 pages, 19 figures. Submitted to ApJ. Revisions on the manuscript will be made during and after peer review

Subject: Astrophysics - Astrophysics of Galaxies