Volume 521, October 2010
Herschel/HIFI: first science highlights
|Number of page(s)||5|
|Published online||01 October 2010|
Letter to the Editor
Reversal of infall in SgrB2(M) revealed by Herschel/HIFI observations of HCN lines at THz frequencies*
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: firstname.lastname@example.org
2 I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
3 Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA
4 SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV, Groningen, The Netherlands
5 California Institute of Technology, Cahill Center for Astronomy and Astrophysics 301-17, Pasadena, CA 91125, USA
6 California Institute of Technology, Division of Geological and Planetary Sciences, MS 150-21, Pasadena, CA 91125, USA
7 Centre d'Étude Spatiale des Rayonnements, Université de Toulouse [UPS], 31062 Toulouse Cedex 9, France
8 CNRS/INSU, UMR 5187, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 4, France
9 Laboratoire d'Astrophysique de l'Observatoire de Grenoble, BP 53, 38041 Grenoble Cedex 9, France
10 Centro de Astrobiología (CSIC/INTA), Laboratorio de Astrofísica Molecular, Ctra. de Torrejón a Ajalvir km 4, 28850 Madrid, Spain
11 LERMA, CNRS UMR8112, Observatoire de Paris and École Normale Supérieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France
12 LPMAA, UMR7092, Université Pierre et Marie Curie, Paris, France
13 LUTH, UMR8102, Observatoire de Paris, Meudon, France
14 Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
15 Departments of Physics, Astronomy and Chemistry, Ohio State University, Columbus, OH 43210, USA
16 National Research Council Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
17 Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
18 Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St George St, Toronto, ON M5S 3H8, Canada
19 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
20 National University of Ireland Maynooth, Ireland
21 Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
22 Observatorio Astronómico Nacional (IGN), Centro Astronómico de Yebes, Apartado 148, 19080 Guadalajara, Spain
23 Departamento de Astrofìsica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, Calle Serrano 121, 28006 Madrid, Spain
24 Microwave Laboratory, ETH Zurich, 8092 Zurich, Switzerland
25 Chalmers University of Technology, 412 96 Göteborg, Sweden, Sweden
26 Department of Astronomy, Stockholm University, 106 91 Stockholm, Sweden
Accepted: 7 July 2010
Aims. To investigate the accretion and feedback processes in massive star formation, we analyze the shapes of emission lines from hot molecular cores, whose asymmetries trace infall and expansion motions.
Methods. The high-mass star forming region SgrB2(M) was observed with Herschel/HIFI (HEXOS key project) in various lines of HCN and its isotopologues, complemented by APEX data. The observations are compared to spherically symmetric, centrally heated models with density power-law gradient and different velocity fields (infall or infall+expansion), using the radiative transfer code RATRAN.
Results. The HCN line profiles are asymmetric, with the emission peak shifting from blue to red with increasing J and decreasing line opacity (HCN to H13CN). This is most evident in the HCN 12–11 line at 1062 GHz. These line shapes are reproduced by a model whose velocity field changes from infall in the outer part to expansion in the inner part.
Conclusions. The qualitative reproduction of the HCN lines suggests that infall dominates in the colder, outer regions, but expansion dominates in the warmer, inner regions. We are thus witnessing the onset of feedback in massive star formation, starting to reverse the infall and finally disrupting the whole molecular cloud. To obtain our result, the THz lines uniquely covered by HIFI were critically important.
Key words: stars: formation / ISM: kinematics and dynamics / ISM: structure / ISM: molecules / ISM: individual objects: SgrB2(M) / submillimeter: ISM
© ESO, 2010
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