Journal
ASTRONOMY & ASTROPHYSICS
Volume 543, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201219449
Keywords
astrochemistry; ISM: clouds; ISM: molecules; ISM: individual objects: Horsehead nebula; radio lines: ISM
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Funding
- Chilean Government through the Becas Chile scholarship program
- French Agence Nationale de la Recherche as part of the SCHISM project [ANR-09-BLAN-0231-01]
- Spanish MICINN [AYA2009-07304, CSD2009-00038]
- Ramon y Cajal research contract from the Spanish MICINN
- European Social Fund
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C+ is a key species in the interstellar medium, but its 158 mu m fine structure line cannot be observed from ground-based telescopes. Current models of fluorine chemistry predict that CF+ is the second-most important fluorine reservoir in regions where C+ is abundant. We detected the J = 1-0 and J = 2-1 rotational lines of CF+ with high signal-to-noise ratio toward the photo-dissociation region and dense core positions in the Horsehead. Using a rotational diagram analysis, we derive a column density of N(CF+) = (1.5-2.0) x 10(12) cm(-2). Because of the simple fluorine chemistry, the CF+ column density is proportional to the fluorine abundance. We thus infer the fluorine gas-phase abundance to be F/H = (0.6-1.5) x 10(-8). Photochemical models indicate that CF+ is found in the layers where C+ is abundant. The emission arises in the UV-illuminated skin of the nebula, tracing the outermost cloud layers. Indeed, CF+ and C+ are the only species observed to date in the Horsehead with a double-peaked line profile caused by kinematics. We therefore propose that CF+, which is detectable from the ground, can be used as a proxy of the C+ layers.
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