The Herschel^⋆, view of massive star formation in G035.39–00.33: dense and cold filament of W48 undergoing a mini-starburst^⋆⋆

¹ Laboratoire AIM Paris-Saclay, CEA/IRFU, CNRS/INSU, Université Paris Diderot, Service d’Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
e-mail: quang.nguyen-luong@cea.fr
² INAF-IFSI, via del Fosso del Cavaliere 100, 00133 Roma, Italy
³ Laboratoire d’Astrophysique de Bordeaux, CNRS/INSU – Université de Bordeaux, BP 89, 33271 Floirac Cedex, France
⁴ Laboratoire d’Astrophysique de Marseille , CNRS/INSU – Université de Provence, 13388 Marseille Cedex 13, France
⁵ Physics Department, West Virginia University, Morgantown, WV 26506, USA
⁶ National Research Council of Canada, Herzberg Institute of Astrophysics, University of Victoria, Department of Physics and Astronomy, Victoria, Canada
⁷ Cardiff University School of Physics and Astronomy, UK
⁸ CITA and Dep. of Astronomy and Astrophysics, University of Toronto, Toronto, Canada
⁹ ESO, Karl Schwarzschild Str. 2, 85748 Garching, Germany
¹⁰ Institut d’Astrophysique de Paris, UMR 7095 CNRS, Université Pierre & Marie Curie, 98bis boulevard Arago, 75014 Paris, France
¹¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹² The Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0NL, UK
¹³ Department of Physics and Astronomy, The Open University, Milton Keynes, UK

Received: 5 August 2011
Accepted: 16 September 2011

Abstract

The filament IRDC G035.39–00.33 in the W48 molecular complex is one of the darkest infrared clouds observed by Spitzer. It has been observed by the PACS (70 and 160 μm) and SPIRE (250, 350, and 500 μm) cameras of the Herschel Space Observatory as part of the W48 molecular cloud complex in the framework of the HOBYS key programme. The observations reveal a sample of 28 compact sources (deconvolved FWHM sizes  < 0.3 pc) complete down to  ~5 M_⊙ in G035.39–00.33 and its surroundings. Among them, 13 compact sources are massive dense cores with masses  >20 M_⊙. The cloud characteristics we derive from the analysis of their spectral energy distributions are masses of 20−50 M_⊙, sizes of 0.1–0.2 pc, and average densities of 2−20 × 10⁵ cm^-3, which make these massive dense cores excellent candidates to form intermediate- to high-mass stars. Most of the massive dense cores are located inside the G035.39–00.33 ridge and host IR-quiet high-mass protostars. The large number of protostars found in this filament suggests that we are witnessing a mini-burst of star formation with an efficiency of  ~15% and a rate density of  ~40 M_⊙ yr^-1kpc^-2 within  ~8 pc², a large area covering the full ridge. Part of the extended SiO emission observed towards G035.39–00.33 is not associated with obvious protostars and may originate from low-velocity shocks within converging flows, as advocated by previous studies.