Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction
Journal article, 2010
We report the detection of absorption by interstellar hydroxyl cations and water cations, along the sight-line to the bright continuum source W49N. We have used Herschel's HIFI instrument, in dual beam switch mode, to observe the 972 GHz N = 1-0 transition of OH+ and the 1115 GHz 1(11)-0(00) transition of ortho-H2O+. The resultant spectra show absorption by ortho-H2O+, and strong absorption by OH+, in foreground material at velocities in the range 0 to 70 km s(-1) with respect to the local standard of rest. The inferred OH+/H2O+ abundance ratio ranges from similar to 3 to similar to 15, implying that the observed OH+ arises in clouds of small molecular fraction, in the 2-8% range. This conclusion is confirmed by the distribution of OH+ and H2O+ in Doppler velocity space, which is similar to that of atomic hydrogen, as observed by means of 21 cm absorption measurements, and dissimilar from that typical of other molecular tracers. The observed OH+/H abundance ratio of a few x10(-8) suggests a cosmic ray ionization rate for atomic hydrogen of 0.6-2.4 x 10(-16) s(-1), in good agreement with estimates inferred previously for diffuse clouds in the Galactic disk from observations of interstellar H-3(+) and other species.
model
line
astrochemistry
laser magnetic-resonance
cation
gas
star-forming regions
ISM: molecules
submillimeter: ISM
h-3(+)
molecular processes
absorption
Author
D. A. Neufeld
Johns Hopkins University
J. R. Goicoechea
Centro de Astrobiologia (CAB)
P. Sonnentrucker
Johns Hopkins University
John H Black
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
J. C. Pearson
Jet Propulsion Laboratory, California Institute of Technology
S. Yu
Jet Propulsion Laboratory, California Institute of Technology
T. G. Phillips
California Institute of Technology (Caltech)
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
E. Herbst
Ohio State University
P. B. Rimmer
Ohio State University
M. Gerin
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
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
Jet Propulsion Laboratory, California Institute of Technology
C. Gry
Laboratoire d'Astrophysique de Marseille
H. Gupta
Jet Propulsion Laboratory, California Institute of Technology
P. Hennebelle
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
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
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
A. Cros
University of Toulouse
K. Klein
University of Waterloo
A. Lorenzani
Arcetri Astrophysical Observatory
S. Philipp
German Aerospace Center (DLR)
A. Samoska
Jet Propulsion Laboratory, California Institute of Technology
R. Shipman
Netherlands Institute for Space Research (SRON)
Aggm Tielens
Leiden University
R. Szczerba
Polish Academy of Sciences
J. Zmuidzinas
California Institute of Technology (Caltech)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 521 1 Article Number: L10- L10Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1051/0004-6361/201015077