Interstellar OH+, H2O+ and H3O+ along the sight-line to G10.6-0.4
Perault, M.; Boulanger, F.; Falgarone, E.; Godard, B.; Contursi, A.; Teyssier, D.; Lis, D. C.; Phillips, T. G.; Bell, T. A.; Cernicharo, J.; Encrenaz, P.; Gerin, M.; Goicoechea, J. R.; Goldsmith, P. F.; Gupta, H.; Herbst, E.; Joblin, C.; Neufeld, D. A.; Pearson, J. C.; Plume, R.; Schlemmer, S.; Stutzki, J.; Vastel, C.; Yu, S.; Samoska, L. A.; Schmidt, M.; Menten, K.; Tielens, A. G. G. M.; Sonnentrucker, P.; Martin-Pintado, J.; Mookerjea, B.; Hennebelle, P.; Dartois, E.; Shipman, R.; Lorenzani, A.; Hily-Blant, P.; de Luca, M.; Gry, C.; Coutens, A.; Kazmierczak, M.; Giesen, T.; Monje, R.; Persson, C.; Salez, M.; Rimmer, P. B.; Zmuidzinas, J.; Cros, A.; Black, J.; Krelowski, J.; Philipp-May, S.; Klein, K.; Geballe, T.; Kolos, R.
France, Sweden, Spain, United States, India, Germany, Poland, Canada, Netherlands, Italy
Abstract
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.
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