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- L10

Subject Categories

Astronomy, Astrophysics and Cosmology

DOI

10.1051/0004-6361/201015077

More information

Latest update

11/12/2021