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Detection of hydrogen fluoride absorption in diffuse molecular clouds with Herschel/HIFI: an ubiquitous tracer of molecular gas

Sonnentrucker, P. and Phillips, T. G. and Lis, D. C. and Bell, T. A. and Monje, R. and Morris, P. (2010) Detection of hydrogen fluoride absorption in diffuse molecular clouds with Herschel/HIFI: an ubiquitous tracer of molecular gas. Astronomy and Astrophysics, 521 . L12. ISSN 0004-6361. doi:10.1051/0004-6361/201015082.

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We discuss the detection of absorption by interstellar hydrogen fluoride (HF) along the sight line to the submillimeter continuum sources W49N and W51. We have used Herschel's HIFI instrument in dual beam switch mode to observe the 1232.4762 GHz J = 1–0 HF transition in the upper sideband of the band 5a receiver. We detected foreground absorption by HF toward both sources over a wide range of velocities. Optically thin absorption components were detected on both sight lines, allowing us to measure – as opposed to obtain a lower limit on – the column density of HF for the first time. As in previous observations of HF toward the source G10.6–0.4, the derived HF column density is typically comparable to that of water vapor, even though the elemental abundance of oxygen is greater than that of fluorine by four orders of magnitude. We used the rather uncertain N(CH)–N(H_2) relationship derived previously toward diffuse molecular clouds to infer the molecular hydrogen column density in the clouds exhibiting HF absorption. Within the uncertainties, we find that the abundance of HF with respect to H_2 is consistent with the theoretical prediction that HF is the main reservoir of gas-phase fluorine for these clouds. Thus, hydrogen fluoride has the potential to become an excellent tracer of molecular hydrogen, and provides a sensitive probe of clouds of small H_2 column density. Indeed, the observations of hydrogen fluoride reported here reveal the presence of a low column density diffuse molecular cloud along the W51 sight line, at an LSR velocity of ~24 km s^(-1), that had not been identified in molecular absorption line studies prior to the launch of Herschel.

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Lis, D. C.0000-0002-0500-4700
Additional Information:© 2010 ESO. Received 29 May 2010; Accepted 13 July 2010; Published online 01 October 2010. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada and the United States under the leadership of SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France and the US. Consortium members are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri- INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiologá (CSIC-INTA). Sweden: Chalmers University of Technology – MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University – Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. M.S. acknowledges support from grant N 203 393334 from Polish MNiSW. This research was performed in part through a JPL contract funded by the National Aeronautics and Space Administration.
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Ministerstwo Nauki i Szkolnictwa Wyższego (MNiSW)N 203 393334
Subject Keywords:molecular processes; astrochemistry; ISM: molecules; submillimeter: ISM
Record Number:CaltechAUTHORS:20110103-110219987
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Official Citation:Detection of hydrogen fluoride absorption in diffuse molecular clouds with Herschel/HIFI: an ubiquitous tracer of molecular gas P. Sonnentrucker, D. A. Neufeld, T. G. Phillips, M. Gerin, D. C. Lis, M. De Luca, J. R. Goicoechea, J. H. Black, T. A. Bell, F. Boulanger, J. Cernicharo, A. Coutens, E. Dartois, M. Kaźmierczak, P. Encrenaz, E. Falgarone, T. R. Geballe, T. Giesen, B. Godard, P. F. Goldsmith, C. Gry, H. Gupta, P. Hennebelle, E. Herbst, P. Hily-Blant, C. Joblin, R. Kołos, J. Krełowski, J. Martín-Pintado, K. M. Menten, R. Monje, B. Mookerjea, J. Pearson, M. Perault, C. M. Persson, R. Plume, M. Salez, S. Schlemmer, M. Schmidt, J. Stutzki, D. Teyssier, C. Vastel, S. Yu, E. Caux, R. Güsten, W. A. Hatch, T. Klein, I. Mehdi, P. Morris and J. S. Ward A&A 521 L12 (2010) DOI: 10.1051/0004-6361/201015082
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21540
Deposited On:05 Jan 2011 21:10
Last Modified:09 Nov 2021 15:58

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