The Pipe Nebula as seen with Herschel: formation of filamentary structures by large-scale compression?^⋆,⋆⋆

¹ Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, IRFU service d’Astrophysique, C.E. Saclay, Orme des merisiers, 91191 Gif-sur-Yvette, France
e-mail: nicolas.peretto@cea.fr
² Université de Toulouse, UPS, CESR, 9 avenue du colonel Roche, 31028 Toulouse Cedex 4, France
³ National Research Council of Canada, Herzberg Institute of Astrophysics, University of Victoria, Department of Physics and Astronomy, Victoria, Canada
⁴ INAF – Instituto Fisica Spazio Interplanetario, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁵ School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF243 AA, UK
⁶ Institut d’Astrophysique de Paris and Université Pierre et Marie Curie (UPMC), UMR 7095 CNRS, 98 boulevard Arago, 75014 Paris, France
⁷ ESO, Karl Schwarzschild str. 2, 85748 Garching bei Munchen, Germany
⁸ University of Central Lancashire, Jeremiah Horrocks Institute, PR12 HE, UK
⁹ Department of Physical Sciences, The Open University Milton Keynes MK7 6AA, England
¹⁰ RALSpace, The Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0NL, England
¹¹ Laboratoire d’Astrophysique de Marseille UMR6110, CNRS, Université de Provence, 38 rue F. Joliot-Curie, 13388 Marseille, France

Received: 16 December 2011
Accepted: 12 March 2012

Abstract

A growing body of evidence indicates that the formation of filaments in interstellar clouds is a key component of the star formation process. In this paper, we present new Herschel-PACS and SPIRE observations of the B59 and Stem regions in the Pipe Nebula complex, revealing a rich, organized network of filaments. The asymmetric column density profiles observed for several filaments, along with the bow-like edge of B59, indicates that the Pipe Nebula is being compressed from its western side, most likely by the winds from the nearby Sco OB2 association. We suggest that this compressive flow has contributed to the formation of some of the observed filamentary structures. In B59, the only region of the entire Pipe complex showing star formation activity, the same compressive flow has likely enhanced the initial column density of the clump, allowing it to become globally gravitationally unstable. Although more speculative, we propose that gravity has also been responsible for shaping the converging filamentary pattern observed in B59. While the question of the relative impact of large-scale compression and gravity remains open in B59, large-scale compression appears to be a plausible mechanism for the initial formation of filamentary structures in the rest of the complex.