Astronomy and Astrophysics, volume 579A, 12-12 (2015/7-1)
Widespread galactic CF+ absorption: detection toward W49 with the Plateau de Bure Interferometer.
LISZT H.S., GUZMAN V.V., PETY J., GERIN M., NEUFELD D.A. and GRATIER P.
Abstract (from CDS):
We study the usefulness of CF+ as a tracer of the regions where C+ and H2 coexist in the interstellar medium. We used the Plateau de Bure Interferometer to synthesize CF+ J=1-0 absorption at 102.6GHz toward the core of the distant HII region W49N at l=43.2°, b=0.0°, and we modeled the fluorine chemistry in diffuse/translucent molecular gas. We detected CF+ absorption over a broad range of velocity showing that CF+ is widespread in the H2-bearing Galactic disk gas. Originally detected in dense gas in the Orion Bar and Horsehead PDR (Photon-Dominated Region) CF+ was subsequently detected in absorption from diffuse and translucent clouds seen toward BL Lac and 3C111. Here we showed that CF+ is distributed throughout the diffuse and translucent molecular disk gas with N(CF+/N(H2)=1.5-2.0x10–10, increasing to N(CF+/N(H2)=3.5x10–10 in one cloud at 39km/s having higher N(H2)=3x1021cm–2. Models of the fluorine chemistry reproduce the observed column densities and relative abundance of HF, from which CF+ forms, but generally overpredict the column density of CF+ by factors of 1.4-4. We show that a free space photodissociation rate Γ>10–9s–1, comparable to that of CH, might account for much of the discrepancy but a recent calculation finds a value about ten times smaller. In the heavily blended and kinematically complex spectra seen toward W49, CF+ absorption primarily traces the peaks of the H2 distribution.