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Chemical Analysis of a Diffuse Cloud along a Line of Sight toward W51: Molecular Fraction and Cosmic-Ray Ionization Rate

N. Indriolo ; D. A. Neufeld ; M. Gerin ; T. R. Geballe ; John H. Black (Institutionen för rymd- och geovetenskap, Radioastronomi och astrofysik) ; K. M. Menten ; J. R. Goicoechea
Astrophysical Journal (0004-637X). Vol. 758 (2012), 2, p. 83 (1-8).
[Artikel, refereegranskad vetenskaplig]

Absorption lines from the molecules OH+, H2O+, and H-3(+) have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH+ and H2O+ are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray ionization rate of atomic hydrogen. H-3(+) is used to infer the cosmic-ray ionization rate of H-2 in the molecular interior of the cloud, which we find to be zeta(2) = (4.8 +/- 3.4) x 10(-16) s(-1). Combining the results from all three species we find an efficiency factor-defined as the ratio of the formation rate of OH+ to the cosmic-ray ionization rate of H-of epsilon = 0.07+/-0.04, much lower than predicted by chemical models. This is an important step in the future use of OH+ and H2O+ on their own as tracers of the cosmic-ray ionization rate.

Nyckelord: astrochemistry, cosmic rays, ISM: molecules, star-forming regions, absorption-line, galactic-center, dissociative, recombination, interstellar oh+, translucent clouds, ions, hydrogen, h-3(+), h2o+



Denna post skapades 2012-12-12. Senast ändrad 2014-09-02.
CPL Pubid: 167573

 

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