Tuesday 06/05/3012

The IRAM-30m line survey of the Horsehead PDR: I. CF+ as a tracer of C+ and a measure of the Fluorine abundance

Authors: V. Guzmán, J. Pety, P. Gratier, J.R. Goicoechea, M. Gerin, E. Roueff, D. Teyssier
(Submitted on 2 Jun 2012)
Abstract: 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 towards the PDR and dense core positions in the Horsehead. Using a rotational diagram analysis, we derive a column density of N(CF+) = (1.5 – 2.0) \times 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) \times 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.

Comments: Accepted to A&A, 4 pages, 4 figures, 2 tables
Subjects: Galaxy Astrophysics (astro-ph.GA)
Cite as: arXiv:1206.0403v1 [astro-ph.GA]

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