The SEDIGISM survey: A search for molecular outflows^★

¹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: ayyang@mpifr-bonn.mpg.de
² Centre for Astrophysics and Planetary Science, University of Kent, Canterbury CT2 7NH, UK
³ School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
⁴ School of Physics and Astronomy, Cardiff University, Cardiff CF24 3AA, UK
⁵ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Laboratoire d’astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁷ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK
⁸ Space Science Institute, 4765 Walnut Street Suite B, Boulder, CO 80301, USA
⁹ Istituto di Astrofisica e Planetologia Spaziali, INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy
¹⁰ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
¹² Department of Astronomy, University of Florida, PO Box 112055, USA
¹³ Korea Astronomy and Space Science Institute, 776 Daedeok-daero, 34055 Daejeon, Republic of Korea
¹⁴ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
¹⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁶ School of Science and Technology, University of New England, Armidale NSW 2351, Australia

Received: 17 August 2021
Accepted: 19 November 2021

Abstract

Context. The formation processes of massive stars are still unclear, but a picture is emerging involving accretion disks and molecular outflows in what appears to be a scaled-up version of low-mass star formation. A census of outflow activity toward high-mass star-forming clumps in various evolutionary stages has the potential to shed light on high-mass star formation.

Aims. We conducted an outflow survey toward ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) clumps using SEDIGISM (structure, Excitation, and Dynamics of the Inner Galactic InterStellar Medium) data and aimed to obtain a large sample of clumps exhibiting outflow activity in different evolutionary stages.

Methods. We identify the high-velocity wings of the ¹³CO lines, which indicate outflow activity, toward ATLASGAL clumps by (1) extracting the simultaneously observed ¹³CO (2–1) and C¹⁸O (2–1) spectra from SEDIGISM, and (2) subtracting Gaussian fits to the scaled C¹⁸O (core emission) from the ¹³CO line after considering opacity broadening.

Results. We detected high-velocity gas toward 1192 clumps out of a total sample of 2052, corresponding to an overall detection rate of 58%. Outflow activity has been detected in the earliest (apparently) quiescent clumps (i.e., 70 μm weak) to the most evolved H II region stages (i.e., 8 μm bright with tracers of massive star formation). The detection rate increases as a function of evolution (quiescent = 51%, protostellar = 47%, YSO = 57%, UC H II regions = 76%).

Conclusions. Our sample is the largest outflow sample identified so far. The high detection rate from this large sample is consistent with the results of similar studies reported in the literature and supports the scenario that outflows are a ubiquitous feature of high-mass star formation. The lower detection rate in early evolutionary stages may be due to the fact that outflows in the early stages are weak and difficult to detect. We obtain a statistically significant sample of outflow clumps for every evolutionary stage, especially for outflow clumps in the earliest stage (i.e., 70 μm dark). The detections of outflows in the 70 μm dark clumps suggest that the absence of 70 μm emission is not a robust indicator of starless and/or pre-stellar cores.