Volume 521, October 2010
Herschel/HIFI: first science highlights
|Number of page(s)||7|
|Published online||01 October 2010|
Letter to the Editor
Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10.6–0.4 (W31C), W49N, and W51 *,**
LERMA, CNRS, Observatoire de Paris and ENS, France e-mail: email@example.com
2 Centro de Astrobiología, CSIC-INTA, Madrid, Spain
3 Depts. of Physics, Astronomy & Chemistry, Ohio State Univ., USA
4 Institut d'Astrophysique Spatiale (IAS), Orsay, France
5 California Institute of Technology, Pasadena, CA 91125, USA
6 Université de Toulouse; UPS; CESR; 9 avenue du colonel Roche, 31028 Toulouse Cedex 4, France
7 CNRS; UMR5187; 31028 Toulouse, France
8 Nicolaus Copernicus University, Torún, Poland
9 The Johns Hopkins University, Baltimore, MD 21218, USA
10 Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
11 JPL, California Institute of Technology, Pasadena, USA
12 I. Physikalisches Institut, University of Cologne, Germany
13 Laboratoire d'Astrophysique de Marseille (LAM), France
14 Laboratoire d'Astrophysique de Grenoble, France
15 Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland
16 Tata Institute of Fundamental Research, Mumbai, India
17 Dept. of Physics & Astronomy, University of Calgary, Canada
18 Nicolaus Copernicus Astronomical Center, Poland
19 European Space Astronomy Centre, ESA, Madrid, Spain
20 MPI für Extraterrestrische Physik, Garching, Germany
21 MPI für Radioastronomie, Bonn, Germany
22 Gemini telescope, Hilo, Hawaii, USA
23 Infrared Processing and Analysis Center, California Institute of Technology, MS 100-22, Pasadena, CA 91125, USA
24 SRON Netherlands Institute for Space Research, Netherlands
Accepted: 9 July 2010
We report the detection of the ground state N,J = 1,3/2 1,1/2 doublet of the methylidyne radical CH at ~532 GHz and ~536 GHz with the Herschel/HIFI instrument along the sight-line to the massive star-forming regions G10.6–0.4 (W31C), W49N, and W51. While the molecular cores associated with these massive star-forming regions show emission lines, clouds in the diffuse interstellar medium are detected in absorption against the strong submillimeter background. The combination of hyperfine structure with emission and absorption results in complex profiles, with overlap of the different hyperfine components. The opacities of most of the CH absorption features are linearly correlated with those of CCH, CN, and HCO+ in the same velocity intervals. In specific narrow velocity intervals, the opacities of CN and HCO+ deviate from the mean trends, giving rise to more opaque absorption features. We propose that CCH can be used as another tracer of the molecular gas in the absence of better tracers, with [CCH]/[ H2] ~ 3.2±1.1×10-8. The observed [CN]/[CH], [CCH]/[CH] abundance ratios suggest that the bulk of the diffuse matter along the lines of sight has gas densities nH = n(H) + 2n(H2) ranging between 100 and 1000 cm-3.
Key words: ISM: clouds / ISM: molecules / submillimeter: ISM / ISM: individual objects: G10.6-0.4 / ISM: individual objects: W49N / ISM: individual objects: W51
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Appendices A and B (pages 6, 7) are only available in electronic form at http://www.aanda.org
© ESO, 2010
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