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Subsonic islands within a high-mass star-forming infrared dark cloud

Sokolov, V, Wang, K, Pineda, JE, Caselli, P, Henshaw, JD, Barnes, AT, Tan, JC, Fontani, F, Jimenez-Serra, I and Zhang, Q (2018) Subsonic islands within a high-mass star-forming infrared dark cloud. Astronomy & Astrophysics, 611. ISSN 1432-0746

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High-mass star forming regions are typically thought to be dominated by supersonic motions. We present combined Very Large Array and Green Bank Telescope (VLA+GBT) observations of NH3 (1,1) and (2,2) in the infrared dark cloud (IRDC) G035.39-00.33, tracing cold and dense gas down to scales of 0.07 pc. We find that, in contrast to previous, similar studies of IRDCs, more than a third of the fitted ammonia spectra show subsonic non-thermal motions (mean line width of 0.71 km s and the sonic Mach number distribution peaks around M = 1. As possible observational and instrumental biases would only broaden the line profiles, our results provide strong upper limits to the actual value of M, further strengthening our findings of narrow line widths. This finding calls for a reevaluation of the role of turbulent dissipation and subsonic regions in massive-star and cluster formation. Based on our findings in G035.39, we further speculate that the coarser spectral resolution used in the previous VLA NH3 studies may have inhibited the detection of subsonic turbulence in IRDCs. The reduced turbulent support suggests that dynamically important magnetic fields of the 1 mG order would be required to support against possible gravitational collapse. Our results offer valuable input into the theories and simulations that aim to recreate the initial conditions of high-mass star and cluster formation.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: EDP Sciences
Related URLs:
Date Deposited: 09 May 2018 11:23
Last Modified: 04 Sep 2021 02:42
DOI or ID number: 10.1051/0004-6361/201832746
URI: https://researchonline.ljmu.ac.uk/id/eprint/8632
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