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Herschel Observations of Interstellar Chloronium

Neufeld, David A. and Lis, Dariusz and Monje, Raquel and Phillips, Thomas G. (2012) Herschel Observations of Interstellar Chloronium. Astrophysical Journal, 748 (1). p. 37. ISSN 0004-637X. doi:10.1088/0004-637X/748/1/37.

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Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed para-chloronium (H_(2)Cl^+) 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-H^(35)_(2)Cl^+ and para-H^(37)_(2)Cl^+ isotopologues were detected, through observations of their 1_(11)-0_(00) 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 × 10^(13) cm^(–2) and ~1.2 × 10^(13) cm^(–2), respectively, for chloronium in these two sources. We obtained upper limits on the para-H^(35)_(2)Cl^+ line strengths toward H_2 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.

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Neufeld, David A.0000-0001-8341-1646
Lis, Dariusz0000-0002-0500-4700
Additional Information:© 2012 American Astronomical Society. Received 2011 November 19; accepted 2012 January 11; published 2012 March 2. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. HIFI has been designed and built by a consortium of institutes and university departments from across Europe, Canada, and the United States under the leadership of the SRON Netherlands Institute for Space Research, Groningen, The Netherlands and with major contributions from Germany, France, and the U.S. Consortium members, which are: Canada: CSA, U. Waterloo; France: CESR, LAB, LERMA, IRAM; Germany: KOSMA, MPIfR, MPS; Ireland, NUI Maynooth; Italy: ASI, IFSI-INAF, Osservatorio Astrofisico di Arcetri-INAF; Netherlands: SRON, TUD; Poland: CAMK, CBK; Spain: Observatorio Astronómico Nacional (IGN), Centro de Astrobiologá (CSICINTA); Sweden: Chalmers University of Technology–MC2, RSS & GARD; Onsala Space Observatory; Swedish National Space Board, Stockholm University–Stockholm Observatory; Switzerland: ETH Zurich, FHNW; USA: Caltech, JPL, NHSC. Support for this work was provided by NASA through an award issued by JPL/Caltech.
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Subject Keywords:ISM: molecules; molecular processes; submillimeter: ISM
Issue or Number:1
Record Number:CaltechAUTHORS:20120417-095315398
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Official Citation:Herschel Observations of Interstellar Chloronium David A. Neufeld et al. 2012 ApJ 748 37
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:30125
Deposited On:17 Apr 2012 18:35
Last Modified:09 Nov 2021 19:37

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