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Herschel observations of interstellar chloronium

David A. Neufeld ; Evelyne Roueff ; Ronald Snell ; Dariusz Lis ; Arnold O. Benz ; Simon Bruderer ; John H. Black (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; Massimo De Luca ; Maryvonne Gerin ; Paul Goldsmith ; Harshal Gupta ; Nick Indriolo ; Jacques Le Bourlot ; Franck Le Petit ; Bengt Larsson ; Gary J. Melnick ; Karl M. Menten ; Raquel Monje ; Zsofia Nagy ; Thomas G. Phillips ; Aage Sandqvist ; Paule Sonnentrucker ; Floris van der Tak ; Mark G. Wolfire
The Astrophysical Journal (0004-637X). Vol. 748 (2012), 2012 March 20, p. 1-11.
[Artikel, refereegranskad vetenskaplig]

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.

Nyckelord: ISM: molecules; molecular processes; submillimeter: ISM


Article 37



Denna post skapades 2012-03-13. Senast ändrad 2015-02-02.
CPL Pubid: 155834

 

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