Volume 518, July-August 2010
Herschel: the first science highlights
|Number of page(s)||5|
|Published online||16 July 2010|
Letter to the Editor
LERMA, CNRS, Observatoire de Paris and ENS, France e-mail: email@example.com
2 Chalmers University of Technology, Göteborg, Sweden
3 Centro de Astrobiología, CSIC-INTA, Madrid, Spain
4 Depts. of Physics, Astronomy & Chemistry, Ohio State Univ., USA
5 The Johns Hopkins University, Baltimore, MD 21218, USA
6 Institut d'Astrophysique Spatiale (IAS), Orsay, France
7 JPL, California Institute of Technology, Pasadena, USA
8 California Institute of Technology, Pasadena, CA 91125, USA
9 Université de Toulouse; UPS; CESR; 9 avenue du colonel Roche, 31028 Toulouse Cedex 4, France
10 CNRS; UMR5187; 31028 Toulouse, France
11 I. Physikalisches Institut, University of Cologne, Germany
12 Laboratoire d'Astrophysique de Marseille (LAM), France
13 Laboratoire d'Astrophysique de Grenoble, France
14 Nicolaus Copernicus University, Torún, Poland
15 Inst. of Physical Chemistry, Polish Academy of Sciences, Poland
16 Tata Institute of Fundamental Research, Mumbai, India
17 Dept. of Physics & Astronomy, University of Calgary, Canada
18 European Space Astronomy Centre, ESA, Madrid, Spain
19 MPI für Extraterrestrische Physik, Garching, Germany
20 MPI für Radioastronomie, Bonn, Germany
21 Gemini telescope, Hilo, Hawaii, USA
22 Nicolaus Copernicus Astronomical Center, Poland
23 SRON Netherlands Institute for Space Research, The Netherlands
24 Sterrewacht Leiden, The Netherlands
25 Deutsches Zentrum für Luft- und Raumfahrt e. V., Raumfahrt-Agentur, Bonn, Germany
26 Osservatorio Astrofisico di Arcetri-INAF- Florence, Italy
Accepted: 30 April 2010
We report the detection of absorption lines by the reactive ions OH+, H2O+and H3O+ along the line of sight to the submillimeter continuum source G10.6–0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+ at 971 GHz, H2O+ at 1115 and 607 GHz, and H3O+ at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6–0.4 as well as in the molecular gas directly associated with that source. The OH+ spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+ lines remains lower than 1 in the same velocity range, and the H3O+line shows only weak absorption. For LSR velocities between 7 and 50 km s-1 we estimate total column densities of N(OH+) ≥ 2.5 × 1014 cm-2, N(H2O+) ~6 × 1013 cm-2 and N(H3O+) ~4.0 × 1013 cm-2. These detections confirm the role of O+ and OH+ in initiating the oxygen chemistry in diffuse molecular gas and strengthen our understanding of the gas phase production of water. The high ratio of the OH+ by the H2O+ column density implies that these species predominantly trace low-density gas with a small fraction of hydrogen in molecular form.
Key words: ISM: general / ISM: molecules / ISM: clouds
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important particiation from NASA.
Figure 2 is only available in electronic form at http://www.aanda.org
© ESO, 2010
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