The Herschel view of the massive star-forming region NGC 6334^⋆,⋆⋆

¹ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
e-mail: delphine.russeil@oamp.fr
² Laboratoire AIM Paris-Saclay, CEA/DSM – INSU/CNRS – Université Paris Diderot, IRFU/SAp, CEA-Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
³ Department of Physics, West Virginia University, Morgantown, WV 26506, USA
⁴ INAF – Istituto Astrofisica e Planetologia Spaziale, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁵ Laboratoire d’Astrophysique de Bordeaux, OASU – UMR 5804, CNRS – Université de Bordeaux 1, 2 rue de l’Observatoire, BP 89, 33270 Floirac, France
⁶ I. Physik. Insitut, Zülpicher Str. 77, University of Cologne, Germany
⁷ Université de Toulouse, UPS, CESR, 9 av. du colonel Roche, 31028 Toulouse, France
⁸ National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
⁹ National Astronomical Observatories of the Chinese Academy of Sciences, 100012 Beijing, PR China
¹⁰ The Canadian Institute for Theoretical Astrophysics (CITA), University of Toronto, 60 St. George Street, Toronto, Ontario, M5S 3H8, Canada
¹¹ Department of Astrophysics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece
¹² Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98 bis Boulevard Arago, 75014 Paris, France
¹³ ESO, Karl Schwarzschild str. 2, 85748 Garching, Germany
¹⁴ Herschel Science Centre, ESA-ESAC, PO Box 78, 28691 Villanueva de la Caada, Madrid, Spain
¹⁵ Jeremiah Horrocks Institute, University of Central Lancashire, PR1 2HE, UK
¹⁶ Department of Physics and Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
¹⁷ RAL Space, STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK

Received: 9 July 2012
Accepted: 28 March 2013

Abstract

Aims. Fundamental to any theory of high-mass star formation are gravity and turbulence. Their relative importance, which probably changes during cloud evolution, is not known. By investigating the spatial and density structure of the high-mass star-forming complex NGC 6334 we aim to disentangle the contributions of turbulence and gravity.

Methods. We used Herschel PACS and SPIRE imaging observations from the HOBYS key programme at wavelengths of 160, 250, 350, and 500 μm to construct dust temperature and column density maps. Using probability distribution functions (PDFs) of the column density determined for the whole complex and for four distinct sub-regions (distinguished on the basis of differences in the column density, temperature, and radiation field), we characterize the density structure of the complex. We investigate the spatial structure using the Δ-variance, which probes the relative amount of structure on different size scales and traces possible energy injection mechanisms into the molecular cloud.

Results. The Δ-variance analysis suggests that the significant scales of a few parsec that were found are caused by energy injection due to expanding H ii regions, which are numerous, and by the lengths of filaments seen everywhere in the complex. The column density PDFs have a lognormal shape at low densities and a clearly defined power law at high densities for all sub-regions whose slope is linked to the exponent α of an equivalent spherical density distribution. In particular with α = 2.37, the central sub-region is largly dominated by gravity, caused by individual collapsing dense cores and global collapse of a larger region. The collapse is faster than free-fall (which would lead only to α = 2) and thus requires a more dynamic scenario (external compression, flows). The column density PDFs suggest that the different sub-regions are at different evolutionary stages, especially the central sub-region, which seems to be in a more evolved stage.