Strong CH+ J = 1-0 emission and absorption in DR21
Boulanger, F.; Falgarone, E.; Godard, B.; Teyssier, D.; Ossenkopf, V.; Erickson, N.; Phillips, T. G.; Gerin, M.; Stutzki, J.; Kramer, C.; Güsten, R.; Lord, S.; Simon, R.; Risacher, C.; Röllig, M.; Fuente, A.; Benz, A. O.; Harris, A.; Klein, T.; Martin-Pintado, J.; van der Tak, F.; Fich, M.; Jellema, W.; Marston, A.; Pearson, J.; Schmülling, F.; Cabrit, S.; Neufeld, D.; Salez, M.; Martin, P.; Yorke, H.; Lesaffre, P.; Joblin, Ch.
France, Germany, Netherlands, United States, Switzerland, Spain, Canada
Abstract
We report the first detection of the ground-state rotational transition of the methylidyne cation CH+ towards the massive star-forming region DR 21 with the HIFI instrument onboard the Herschel satellite. The line profile exhibits a broad emission line, in addition to two deep and broad absorption features associated with the DR 21 molecular ridge and foreground gas. These observations allow us to determine a 12CH+J = 1-0 line frequency of ν = 835 137 ± 3 MHz, in good agreement with a recent experimental determination. We estimate the CH+ column density to be a few 1013 cm-2 in the gas seen in emission, and >1014 cm-2 in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH+] /[H] > 1.2 × 10-8. We show that the CH+ column densities agree well with the predictions of state-of-the-art C-shock models in dense UV-illuminated gas for the emission line, and with those of turbulent dissipation models in diffuse gas for the absorption lines.
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.