Herschel observations of interstellar chloronium
Artikel i vetenskaplig tidskrift, 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.

ISM: molecules

molecular processes

submillimeter: ISM


D. A. Neufeld

Johns Hopkins University

Evelyne Roueff

Observatoire de Paris-Meudon

Ronald Snell

University of Massachusetts

D. C. Lis


A. O. Benz

Eidgenössische Technische Hochschule Zürich (ETH)

S. Bruderer

Max Planck-institutet

John H Black

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

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 University of Technology

G. J. Melnick

Harvard-Smithsonian Center for Astrophysics

K. M. Menten

Max Planck-institutet

Raquel Rodriguez-Monje


Zsofia Nagy

University of Groningen, Kapteyn Astronomical Institute

T.G. Phillips


A. Sandqvist

Stockholm Observatory

P. Sonnentrucker


F. F. S. van der Tak

University of Groningen, Kapteyn Astronomical Institute

SRON Netherlands Institute for Space Research

M. Wolfire

University of Maryland

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 748 1-11 37


Astronomi, astrofysik och kosmologi


Grundläggande vetenskaper


Onsala rymdobservatorium