We use molecular line data from the Atacama Large Millimeter/submillimeter Array, Submillimeter Array, James Clerk Maxwell Telescope, and NANTEN2 to study the multiscale (∼15–0.005 pc) velocity statistics in the massive star formation region NGC 6334. We find that the nonthermal motions revealed by the velocity dispersion function (VDF) stay supersonic over scales of several orders of magnitude. The multiscale nonthermal motions revealed by different instruments do not follow the same continuous power law, which is because the massive star formation activities near central young stellar objects have increased the nonthermal motions in small-scale and high-density regions. The magnitudes of VDFs vary in different gas materials at the same scale, where the infrared dark clump N6334S in an early evolutionary stage shows a lower level of nonthermal motions than other more evolved clumps due to its more quiescent star formation activity. We find possible signs of small-scale-driven (e.g., by gravitational accretion or outflows) supersonic turbulence in clump N6334IV with a three-point VDF analysis. Our results clearly show that the scaling relation of velocity fields in NGC 6334 deviates from a continuous and universal turbulence cascade due to massive star formation activities.
We present a study of molecular structures (clumps and clouds) in the dwarf galaxy NGC 404 using high-resolution (≈0.86 × 0.51 pc2) Atacama Large Millimeter/sub-millimeter Array 12CO(2-1) observations. We find two distinct regions in NGC 404: a gravitationally stable central region (Toomre parameter Q = 3–30) and a gravitationally unstable molecular ring (Q ≲ 1). The molecular structures in the central region have a steeper size–linewidth relation and larger virial parameters than those in the molecular ring, suggesting gas is more turbulent in the former. In the molecular ring, clumps exhibit a shallower mass–size relation and larger virial parameters than clouds, implying density structures and dynamics are regulated by different physical mechanisms at different spatial scales. We construct an analytical model of clump–clump collisions to explain the results in the molecular ring. We propose that clump–clump collisions are driven by gravitational instabilities coupled with galactic shear, which lead to a population of clumps whose accumulation lengths (i.e. average separations) are approximately equal to their tidal radii. Our model-predicted clump masses and sizes (and mass–size relation) and turbulence energy injection rates (and size–linewidth relation) match the observations in the molecular ring very well, suggesting clump–clump collisions are the main mechanism regulating clump properties and gas turbulence in that region. As expected, our collision model does not apply to the central region, where turbulence is likely driven by clump migration.
more » « less- NSF-PAR ID:
- 10373072
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 517
- Issue:
- 1
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 632-656
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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