Detection of hydrogen fluoride absorption in diffuse molecular clouds with Herschel/HIFI: an ubiquitous tracer of molecular gas
Journal article, 2010
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 similar to 24 km s(-1), that had not been identified in molecular absorption line studies prior to the launch of Herschel.
astronomy
line-of-sight
astrochemistry
submillimeter: ISM
abundance
w51
w49n
h2o
co
regions
molecular processes
ISM: molecules
Author
P. Sonnentrucker
Johns Hopkins University
D. A. Neufeld
Johns Hopkins University
T. G. Phillips
California Institute of Technology (Caltech)
M. Gerin
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
D. C. Lis
California Institute of Technology (Caltech)
M. de Luca
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
J. R. Goicoechea
Centro de Astrobiologia (CAB)
John H Black
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
T. A. Bell
California Institute of Technology (Caltech)
F. Boulanger
Institut d'Astrophysique Spatiale
J. Cernicharo
Centro de Astrobiologia (CAB)
A. Coutens
University of Toulouse
E. Dartois
Institut d'Astrophysique Spatiale
M. Kazmierczak
Nicolaus Copernicus University
P. Encrenaz
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
E. Falgarone
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
T. R. Geballe
Gemini Observatory North
T. Giesen
University of Cologne
B. Godard
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
P. F. Goldsmith
California Institute of Technology (Caltech)
C. Gry
Laboratoire d'Astrophysique de Marseille
H. Gupta
California Institute of Technology (Caltech)
P. Hennebelle
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
E. Herbst
Ohio State University
P. Hily-Blant
Laboratoire d'Astrophysique de Grenoble
C. Joblin
University of Toulouse
R. Kolos
Polish Academy of Sciences
J. Krelowski
Nicolaus Copernicus University
J. Martin-Pintado
Centro de Astrobiologia (CAB)
K. M. Menten
Max Planck Society
Raquel Monje
California Institute of Technology (Caltech)
B. Mookerjea
Tata Institute of Fundamental Research
J. C. Pearson
California Institute of Technology (Caltech)
M. Perault
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
Carina Persson
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
R. Plume
University of Calgary
M. Salez
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
S. Schlemmer
University of Cologne
M. Schmidt
Polish Academy of Sciences
J. Stutzki
University of Cologne
D. Teyssier
European Space Astronomy Centre (ESAC)
C. Vastel
University of Toulouse
S. Yu
California Institute of Technology (Caltech)
E. Caux
University of Toulouse
R. Güsten
Max Planck Society
W. A. Hatch
California Institute of Technology (Caltech)
T. Klein
Max Planck Society
Imran Mehdi
California Institute of Technology (Caltech)
P. Morris
California Institute of Technology (Caltech)
J. S. Ward
California Institute of Technology (Caltech)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 521 1 Article Number: L12- L12Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201015082