HERSCHEL OBSERVATIONS OF INTERSTELLAR CHLORONIUM

Journal Article · Tue Mar 20 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/748/1/37· OSTI ID:22016177

Neufeld, David A; Indriolo, Nick ^[1]; Roueff, Evelyne; Le Bourlot, Jacques; Le Petit, Franck ^[2]; Snell, Ronald L ^[3]; Lis, Dariusz; Monje, Raquel; Phillips, Thomas G ^[4]; Benz, Arnold O ^[5]; Bruderer, Simon ^[6]; Black, John H; Larsson, Bengt ^[7]; De Luca, Massimo; Gerin, Maryvonne ^[8]; Goldsmith, Paul F; Gupta, Harshal ^[9]; Melnick, Gary J ^[10]; Menten, Karl M ^[11]; Nagy, Zsofia ^[12] ; others, and

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1. Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218 (United States)
2. Observatoire de Paris-Meudon, LUTH UMR 8102, 5 Pl. Jules Janssen, F-92195 Meudon Cedex (France)
3. Astronomy Department, University of Massachusetts at Amherst, Amherst, MA 01003 (United States)
4. Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
5. Institute of Astronomy, ETH Zurich, 8092 Zurich (Switzerland)
6. Max Planck Institut fuer Extraterrestrische Physik, Giessenbachstrasse 1, D-85748, Garching (Germany)
7. Department of Earth and Space Sciences, Chalmers University of Technology, Onsala (Sweden)
8. LERMA, UMR 8112 du CNRS, Observatoire de Paris, Ecole Normale Superieure, UPMC and UCP (France)
9. JPL, California Institute of Technology, Pasadena, CA (United States)
10. Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
11. Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)
12. Kapteyn Astronomical Institute University of Groningen, Groningen (Netherlands)

Using the Herschel Space Observatory's Heterodyne Instrument for the Far-Infrared, we have observed para-chloronium (H{sub 2}Cl{sup +}) 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{sup -1} cloud) and W31C. Both the para-H{sup 35}{sub 2}Cl{sup +} and para-H{sup 37}{sub 2}Cl{sup +} isotopologues were detected, through observations of their 1{sub 11}-0{sub 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 {approx}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 {approx}2 Multiplication-Sign 10{sup 13} cm{sup -2} and {approx}1.2 Multiplication-Sign 10{sup 13} cm{sup -2}, respectively, for chloronium in these two sources. We obtained upper limits on the para-H{sup 35}{sub 2}Cl{sup +} line strengths toward H{sub 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 {approx}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.

• OSTI ID: 22016177
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 748; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
ABUNDANCE
CHLORINE
GALAXIES
HYDROGEN
PHOTOLYSIS
STARS
STEADY-STATE CONDITIONS