The role of turbulence in high-mass star formation: Subsonic and transonic turbulence are ubiquitously found at early stages

¹ Department of Astronomy, School of Physics, Peking University, Beijing 100871, PR China
e-mail: chaowang3407@pku.edu.cn
² Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
e-mail: kwang.astro@pku.edu.cn
³ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁴ Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ Department of Physics, National Sun Yat-Sen University, No. 70, Lien-Hai Road, Kaohsiung City 80424, Taiwan, ROC
⁶ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
⁷ Max Planck Institute for Extraterrestrial Physics, Giessenbachstr. 1, 85748 Garching, Germany
⁸ INAF Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
⁹ Boston University Astronomy Department, 725 Commonwealth Avenue, Boston, MA 02215, USA
¹⁰ East Asian Observatory, 660 N. A’ohōkū Place, University Park, Hilo, HI 96720, USA
¹¹ Institute of Astronomy and Astrophysics, Academia Sinica, 11F of Astronomy-Mathematics Building, AS/NTU No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan, ROC
¹² Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹³ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), c. Martí i Franquès, 1, 08028 Barcelona, Spain
¹⁴ Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), c. Martí i Franquès, 1, 08028 Barcelona, Spain
¹⁵ Institut d'Estudis Espacials de Catalunya (IEEC), c. Gran Capità, 2–4, 08034 Barcelona, Spain
¹⁶ National Astronomical Observatory of Japan, National Institutes of Natural Sciences, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁷ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
¹⁸ Computational Astronomy Group, Zhejiang Lab, Hangzhou, Zhejiang 311121, PR China
¹⁹ University of Chinese Academy of Sciences, Beijing 100049, PR China
²⁰ SOFIA Science Center, NASA Ames Research Center, Moffett Field, CA 94045, USA
²¹ Green Bank Observatory, PO Box 2, Green Bank, WV 24944, USA
²² Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4235, USA
²³ Department of Space, Earth & Environment, Chalmers University of Technology, 412 96 Gothenburg, Sweden

Received: 26 May 2023
Accepted: 11 October 2023

Abstract

Context. Traditionally, supersonic turbulence is considered to be one of the most likely mechanisms slowing the gravitational collapse in dense clumps, thereby enabling the formation of massive stars. However, several recent studies have raised differing points of view based on observations carried out with sufficiently high spatial and spectral resolution. These studies call for a re-evaluation of the role turbulence plays in massive star-forming regions.

Aims. Our aim is to study the gas properties, especially the turbulence, in a sample of massive star-forming regions with sufficient spatial and spectral resolution, which can both resolve the core fragmentation and the thermal line width.

Methods. We observed NH₃ metastable lines with the Very Large Array (VLA) to assess the intrinsic turbulence.

Results. Analysis of the turbulence distribution histogram for 32 identified NH₃ cores reveals the presence of three distinct components. Furthermore, our results suggest that (1) sub- and transonic turbulence is a prevalent (21 of 32) feature of massive star-forming regions and those cold regions are at early evolutionary stage. This investigation indicates that turbulence alone is insufficient to provide the necessary internal pressure required for massive star formation, necessitating further exploration of alternative candidates; and (2) studies of seven multi-core systems indicate that the cores within each system mainly share similar gas properties and masses. However, two of the systems are characterized by the presence of exceptionally cold and dense cores that are situated at the spatial center of each system. Our findings support the hub-filament model as an explanation for this observed distribution.