Nitrogen hydrides in interstellar gas: Herschel/HIFI observations towards G10.6-0.4 (W31C)

C. M. Persson, J. H. Black, J. Cernicharo, J. R. Goicoechea, G. E. Hassel, E. Herbst, M. Gerin, M. De Luca, T. A. Bell, A. Coutens, E. Falgarone, P. F. Goldsmith, H. Gupta, M. Kazmierczak, D. C. Lis, B. Mookerjea, D. A. Neufeld, J. Pearson, T. G. Phillips, P. Sonnentrucker, J. Stutzki, C. Vastel, S. Yu, F. Boulanger, E. Dartois, P. Encrenaz, T. R. Geballe, T. Giesen, B. Godard, C. Gry, P. Hennebelle, P. Hily-Blant, C. Joblin, R. Kolos, J. Krelowski, J. Martin-Pintado, K. Menten, R. Monje, M. Perault, R. Plume, M. Salez, S. Schlemmer, M. Schmidt, D. Teyssier, I. Peron, P. Cais, P. Gaufre, A. Cros, L. Ravera, P. Morris, S. Lord, P. Planesas

Published 2010-07-15Version 1

The HIFI instrument on board the Herschel Space Observatory has been used to observe interstellar nitrogen hydrides along the sight-line towards G10.6-0.4 in order to improve our understanding of the interstellar chemistry of nitrogen. We report observations of absorption in NH N=1-0, J=2-1 and ortho-NH2 1_1,1-0_0,0. We also observed ortho-NH3 1_0-0_0, and 2_0-1_0, para-NH3 2_1-1_1, and searched unsuccessfully for NH+. All detections show emission and absorption associated directly with the hot-core source itself as well as absorption by foreground material over a wide range of velocities. All spectra show similar, non-saturated, absorption features, which we attribute to diffuse molecular gas. Total column densities over the velocity range 11-54 km/s are estimated. The similar profiles suggest fairly uniform abundances relative to hydrogen, approximately 6*10^-9, 3*10^-9, and 3*10^-9 for NH, NH2, and NH3, respectively. These abundances are discussed with reference to models of gas-phase and surface chemistry.