Volume 602, June 2017
|Number of page(s)||83|
|Section||Interstellar and circumstellar matter|
|Published online||19 June 2017|
The earliest phases of high-mass star formation, as seen in NGC 6334 by Herschel-HOBYS ⋆,⋆⋆
1 Aix-Marseille Univ., CNRS, LAM, Laboratoire d’Astrophysique de Marseille, Marseille, France
2 Université Grenoble Alpes, CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble, 38000 Grenoble, France
3 Laboratoire AIM Paris-Saclay, CEA/IRFU – CNRS/INSU – Université Paris Diderot, Service d’Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
4 Max-Planck-Institut für Astronomie, Königsstuhl 17, 69117 Heidelberg, Germany
5 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée G. Saint-Hilaire, 33615 Pessac, France
6 I. Physik. Institut, University of Cologne, 50937 Cologne, Germany
7 Joint ALMA Observatory, 3107 Alonso de Cordova, Vitacura, Santiago, Chile
8 Korea Astronomy and Space Science Institute, 776 Daedeok daero, Yuseoung, Daejeon 34055, Korea
9 NAOJ Chile Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
10 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
11 Department of Physics and Astronomy, University of Victoria, PO Box 355, STN CSC, Victoria, BC V8W 3P6, Canada
12 Department of Astronomy, Universidad de Chile, Las Condes, Santiago, Chile
13 Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
14 National Radio Astronomy Observatory, PO Box 2, Green Bank, WV 24944, USA
15 INAF-Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, 00133 Rome, Italy
16 Université de Toulouse, UPS-OMP, CNRS, IRAP, 31028 Toulouse Cedex 4, France
17 Jeremiah Horrocks Institute, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK
18 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8, Canada
19 Departamento de Fisica, Universidad de Atacama, Copiapo, Chile
20 Cardiff School of Physics and Astronomy, Cardiff University, Queen’s Buildings, The Parade, Cardiff, Wales, CF24 3AA, UK
21 European Space Astronomy Centre ESA/ESAC, 28691 Villanueva de la Cañada, Madrid, Spain
22 Institut d’Astrophysique de Paris, Sorbonne Universités, UPMC Univ. Paris 06, CNRS UMR 7095, 75014 Paris, France
23 INAF−IRA, via P. Gobetti 101, 40129 Bologna, Italy
24 Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
25 RAL Space, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
Received: 24 May 2016
Accepted: 14 March 2017
Aims. To constrain models of high-mass star formation, the Herschel-HOBYS key program aims at discovering massive dense cores (MDCs) able to host the high-mass analogs of low-mass prestellar cores, which have been searched for over the past decade. We here focus on NGC 6334, one of the best-studied HOBYS molecular cloud complexes.
Methods. We used Herschel/PACS and SPIRE 70−500 μm images of the NGC 6334 complex complemented with (sub)millimeter and mid-infrared data. We built a complete procedure to extract ~0.1 pc dense cores with the getsources software, which simultaneously measures their far-infrared to millimeter fluxes. We carefully estimated the temperatures and masses of these dense cores from their spectral energy distributions (SEDs). We also identified the densest pc-scale cloud structures of NGC 6334, one 2 pc × 1 pc ridge and two 0.8 pc × 0.8 pc hubs, with volume-averaged densities of ~105 cm-3.
Results. A cross-correlation with high-mass star formation signposts suggests a mass threshold of 75 M⊙ for MDCs in NGC 6334. MDCs have temperatures of 9.5−40 K, masses of 75−1000 M⊙, and densities of 1 × 105−7 × 107 cm-3. Their mid-infrared emission is used to separate 6 IR-bright and 10 IR-quiet protostellar MDCs while their 70 μm emission strength, with respect to fitted SEDs, helps identify 16 starless MDC candidates. The ability of the latter to host high-mass prestellar cores is investigated here and remains questionable. An increase in mass and density from the starless to the IR-quiet and IR-bright phases suggests that the protostars and MDCs simultaneously grow in mass. The statistical lifetimes of the high-mass prestellar and protostellar core phases, estimated to be 1−7 × 104 yr and at most 3 × 105 yr respectively, suggest a dynamical scenario of high-mass star formation.
Conclusions. The present study provides good mass estimates for a statistically significant sample, covering the earliest phases of high-mass star formation. High-mass prestellar cores may not exist in NGC 6334, favoring a scenario presented here, which simultaneously forms clouds, ridges, MDCs, and high-mass protostars.
Key words: dust, extinction / ISM: clouds / stars: formation / submillimeter: ISM / stars: protostars / ISM: individual objects: NGC 6334
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Catalogs built from Tables A.1–A.12, are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A77
© ESO, 2017
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