Herschel-HOBYS study of the earliest phases of high-mass star formation in NGC 6357^★,★★

¹ CNRS, CNES, LAM, Aix-Marseille Univ., Marseille, France
e-mail: delphine.russeil@lam.fr
² National Centre for Nuclear Research, ul. Hoza 69, 00-681 Warszawa, Poland
³ CNRS, IPAG, Université Grenoble Alpes, 38000 Grenoble, France
⁴ I. Physik. Institut, University of Cologne, 50937 Cologne, Germany
⁵ Laboratoire d’Astrophysique de Bordeaux, CNRS/INSU, Université de Bordeaux, UMR 5804, France
⁶ Laboratoire AIM, CEA/IRFU CNRS/INSU Université Paris Diderot, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
⁷ Department of Physics and Astronomy, West Virginia University, Morgantown WV 26506, USA
⁸ Adjunct Astronomer at the Green Bank Observatory, PO Box 2, Green Bank WV 24944, USA
⁹ Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Research Building, Morgantown, WV 26505, USA
¹⁰ INAF – IAPS, Via Fosso del Cavaliere 100, 00133 Rome, Italy
¹¹ Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK
¹² Korea Astronomy and Space Science Institute, 776 Daedeok daero, Yuseoung, Daejeon 34055, Korea
¹³ NAOJ Chile Observatory National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁴ INAF – Istituto di Radioastronomia & Italian ALMA Regional Centre, via P. Gobetti 101, 40129 Bologna, Italy
¹⁵ School for Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
¹⁶ RAL Space, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK

Received: 16 July 2018
Accepted: 2 April 2019

Abstract

Aims. To constrain models of high-mass star formation it is important to identify the massive dense cores (MDCs) that are able to form high-mass star(s). This is one of the purposes of the Herschel/HOBYS key programme. Here, we carry out the census and characterise of the properties of the MDCs population of the NGC 6357 H II region.

Methods. Our study is based on the Herschel/PACS and SPIRE 70−500 μm images of NGC 6357 complemented with (sub-)millimetre and mid-infrared data. We followed the procedure established by the Herschel/HOBYS consortium to extract ~0.1 pc massive dense cores using the getsources software. We estimated their physical parameters (temperatures, masses, luminosities) from spectral energy distribution (SED) fitting.

Results. We obtain a complete census of 23 massive dense cores, amongst which one is found to be IR-quiet and twelve are starless, representing very early stages of the star-formation process. Focussing on the starless MDCs, we have considered their evolutionary status, and suggest that only five of them are likely to form a high-mass star.

Conclusions. We find that, contrarily to the case in NGC 6334, the NGC 6357 region does not exhibit any ridge or hub features that are believed to be crucial to the massive star formation process. This study adds support for an empirical model in which massive dense cores and protostars simultaneously accrete mass from the surrounding filaments. In addition, the massive star formation in NGC 6357 seems to have stopped and the hottest stars in Pismis 24 have disrupted the filaments.