Interstellar OH+ , H2O+ and H3O+ along the sight-line to G10.6-0.4

Maryvonne Gerin (1) , M. de Luca (1) , John Black (2) , Eric Herbst (3, 4) , Javier R.Goicoechea (5, 6) , Edith Falgarone (1) , Benjamin Godard (1) , John C. Pearson (7) , Dariucz C. Lis (8) , Thomas G. Phillips (8) , Thomas A. Bell (8) , Paule Sonnentrucker (9) , Francois Boulanger (10) , José Cernicharo (5, 6) , Audrey Coutens (11) , Emmanuel Dartois (10) , Pierre Encrenaz (1) , Thomas Giesen (12) , Paul F. Goldsmith (7) , Harshal Gupta (7) , Cecile Gry (13) , Patrick Hennebelle (1) , Pierre Hily-Blant (14) , Christine Joblin (11) , Maja Kazmierczak (15) , Robert Kolos (16) , Jacek Krelowski (15) , Jesus Martin-Pintado (17) , Raquel Monje (8) , Bhaswati Mookerjea (18) , Michel Pérault (1) , Carina Persson (2) , René Plume (19) , Paul B. Rimmer (3, 4) , Morvan Salez (1) , Mirisloaw Schmidt (20) , David Teyssier (1) , Charlotte Vastel (11) , Shan Shan Yu (7) , Alessandra Contursi (21) , Karl Menten (22) , Thomas Geballe (23) , Stephan Schlemmer (12) , Russ Shipman (24) , Alexander G.G.M. Tielens (25) , Sabine Philipp-May (22, 26) , Alain Cros (27) , Jonas Zmuidzinas (8) , L.A Samoska (7) , K. Klein (26) , D.A. Neufeld (9) , A. Lorenzani (28) , Jürgen Stutzki (12)

1 LERMA - Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique
2 OSO - Onsala Space Observatory
3 OHIO STATE UNIVERSITY - Department of Physics
4 Departments of Astronomy and Chemistry
5 CAB - Centro de Astrobiologia [Madrid]
6 CSIC - Centro de Investigaciones Biológicas
7 JPL - Jet Propulsion Laboratory
8 CSO - CalTech-CSO
9 Department of Physics and Astronomy [Baltimore]
10 IAS - Institut d'astrophysique spatiale
11 CESR - Centre d'étude spatiale des rayonnements
12 I. Physikalisches Institut [Köln]
13 LAM - Laboratoire d'Astrophysique de Marseille
14 LAOG - Laboratoire d'Astrophysique de Grenoble
15 TCfA - Torun Centre for Astronomy
16 Institute of physical chemistry
17 IEM - Instituto de Estructura de la Materia
18 TIFR - Tata Institute for Fundamental Research
19 Department of Physics and Astronomy [Calgary]
20 CAMK - Copernicus Astronomical Center of the Polish Academy of Sciences
21 MPE - Max-Planck-Institut für Extraterrestrische Physik
22 MPIFR - Max-Planck-Institut für Radioastronomie
23 Gemini Telescope
24 SRON - SRON Netherlands Institute for Space Research
25 Sterrewacht Leiden
26 DLR - Deutsches Zentrum für Luft- und Raumfahrt [Bonn]
27 LP3 - Laboratoire Lasers, Plasmas et Procédés photoniques
28 OAA - INAF - Osservatorio Astrofisico di Arcetri

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$-$0.4 (W31C). We used the Herschel HIFI instrument in dual beam switch mode to observe the ground state rotational transitions of OH+ at 971~GHz, H2O+ at 1115 and 607~GHz, and H3O+ at 984 GHz. The resultant spectra show deep absorption over a broad velocity range that originates in the interstellar matter along the line of sight to G10.6$-$0.4 as well as in the molecular gas directly associated with that source. The OH+ spectrum reaches saturation over most velocities corresponding to the foreground gas, while the opacity of the H2O+ lines remains lower than 1 in the same velocity range, and the H3O+ line shows only weak absorption. For LSR velocities between 7 and 50 kms$^{-1}$ we estimate total column densities of $N$(OH+) $> 2.5 \times 10^{14}$ cm$^{-2}$, $N$(H2O+) $\sim 6 \times 10^{13}$ cm$^{-2}$ and $N$(H3O+) $\sim 4.0 \times 10^{13}$ 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.

Domaines: Astrophysique galactique [astro-ph.GA]; Astrophysique galactique [astro-ph.GA]

Maryvonne Gerin, M. de Luca, John Black, Eric Herbst, Javier R.Goicoechea, et al.. Interstellar OH+ , H2O+ and H3O+ along the sight-line to G10.6-0.4. 2010. ⟨hal-00485859⟩