Herschel observations of interstellar chloronium
Journal article, 2012
Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed para-chloronium (H2Cl+) toward six sources in the Galaxy. We detected interstellar chloronium absorption in foreground molecular clouds along the sight lines to the bright submillimeter continuum sources Sgr A (+50 km s–1 cloud) and W31C. Both the para-H35 2Cl+ and para-H37 2Cl+ isotopologues were detected, through observations of their 111-000 transitions at rest frequencies of 485.42 and 484.23 GHz, respectively. For an assumed ortho-to-para ratio (OPR) of 3, the observed optical depths imply that chloronium accounts for ~4%-12% of chlorine nuclei in the gas phase. We detected interstellar chloronium emission from two sources in the Orion Molecular Cloud 1: the Orion Bar photodissociation region and the Orion South condensation. For an assumed OPR of 3 for chloronium, the observed emission line fluxes imply total beam-averaged column densities of ~2 × 1013 cm–2 and ~1.2 × 1013 cm–2, respectively, for chloronium in these two sources. We obtained upper limits on the para-H35 2Cl+ line strengths toward H2 Peak 1 in the Orion Molecular cloud and toward the massive young star AFGL 2591. The chloronium abundances inferred in this study are typically at least a factor ~10 larger than the predictions of steady-state theoretical models for the chemistry of interstellar molecules containing chlorine. Several explanations for this discrepancy were investigated, but none has proven satisfactory, and thus the large observed abundances of chloronium remain puzzling.
submillimeter: ISM
molecular processes
ISM: molecules
Author
D. A. Neufeld
Johns Hopkins University
Evelyne Roueff
Observatoire de Paris-Meudon
Ronald Snell
University of Massachusetts
D. C. Lis
California Institute of Technology (Caltech)
A. O. Benz
Swiss Federal Institute of Technology in Zürich (ETH)
S. Bruderer
Max Planck Society
John H Black
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
Massimo De Luca
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
M. Gerin
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
Paul F. Goldsmith
Jet Propulsion Laboratory, California Institute of Technology
H. Gupta
Jet Propulsion Laboratory, California Institute of Technology
N. Indriolo
Johns Hopkins University
Jacques Le Bourlot
Observatoire de Paris-Meudon
Franck Le Petit
Observatoire de Paris-Meudon
Bengt Larsson
Chalmers, Earth and Space Sciences
G. J. Melnick
Harvard-Smithsonian Center for Astrophysics
K. M. Menten
Max Planck Society
Raquel Monje
California Institute of Technology (Caltech)
Zsofia Nagy
University of Groningen
T.G. Phillips
California Institute of Technology (Caltech)
A. Sandqvist
Stockholm Observatory
P. Sonnentrucker
Space Telescope Science Institute (STScI)
F. F. S. van der Tak
Netherlands Institute for Space Research (SRON)
University of Groningen
M. Wolfire
University of Maryland
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 748 2012 March 20 1-11 37Subject Categories
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
Infrastructure
Onsala Space Observatory
DOI
10.1088/0004-637X/748/1/37