Fragmentation and kinematics in high-mass star formation

CORE-extension targeting two very young high-mass star-forming regions^★

¹ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: beuther@mpia.de
² UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh EH9 3HJ, UK
³ IRAM, 300 rue de la Piscine, Domaine Universitaire de Grenoble, 38406 St.-Martin-d’Hères, France
⁴ Centre for Astrophysics and Planetary Science, University of Kent, Canterbury, CT2 7NH, UK
⁵ Chinese Academy of Sciences Key Laboratory of FAST, National Astronomical Observatory of Cina, Datun Road 20, Chaoyang, Bejing 100012, PR China
⁶ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
⁷ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁸ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK
⁹ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching, Germany
¹⁰ Instituto de Radioastronomıa y Astrofısica, Universidad Nacional Autonoma de Mexico, PO Box 3-72, 58090 Morelia, Michoacan, Mexico
¹¹ School of Physics & Astronomy, E.C. Stoner Building, The University of Leeds, Leeds LS2 9JT, UK
¹² Department of Physics and Astronomy, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4M1, Canada
¹³ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁴ Institute of Astronomy and Astrophysics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
¹⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 10 December 2020
Accepted: 26 February 2021

Abstract

Context. The formation of high-mass star-forming regions from their parental gas cloud and the subsequent fragmentation processes lie at the heart of star formation research.

Aims. We aim to study the dynamical and fragmentation properties at very early evolutionary stages of high-mass star formation.

Methods. Employing the NOrthern Extended Millimeter Array and the IRAM 30 m telescope, we observed two young high-mass star-forming regions, ISOSS22478 and ISOSS23053, in the 1.3 mm continuum and spectral line emission at a high angular resolution (~0.8″).

Results. We resolved 29 cores that are mostly located along filament-like structures. Depending on the temperature assumption, these cores follow a mass-size relation of approximately M ∝ r^{2.0 ± 0.3}, corresponding to constant mean column densities. However, with different temperature assumptions, a steeper mass-size relation up to M ∝ r^{3.0 ± 0.2}, which would be more likely to correspond to constant mean volume densities, cannot be ruled out. The correlation of the core masses with their nearest neighbor separations is consistent with thermal Jeans fragmentation. We found hardly any core separations at the spatial resolution limit, indicating that the data resolve the large-scale fragmentation well. Although the kinematics of the two regions appear very different at first sight – multiple velocity components along filaments in ISOSS22478 versus a steep velocity gradient of more than 50 km s⁻¹ pc⁻¹ in ISOSS23053 – the findings can all be explained within the framework of a dynamical cloud collapse scenario.

Conclusions. While our data are consistent with a dynamical cloud collapse scenario and subsequent thermal Jeans fragmentation, the importance of additional environmental properties, such as the magnetization of the gas or external shocks triggering converging gas flows, is nonetheless not as well constrained and would require future investigation.