Strong CH+ J = 1–0 emission and absorption in DR21

摘要

We report the first detection of the ground-state rotational transition of the methylidyne cation CH+ towards the massive star-forming regionDR21 with the HIFI instrument onboard the Herschelsatellite. The line profile exhibits a broad emission line,inaddition to two deep and broad absorption features associatedwith the DR21 molecular ridge and foreground gas. Theseobservations allow us to determine a ^12CH^+J=1-0 line frequency of = 8351373MHz, ingood agreement with a recent experimental determination. We estimate the CH+column density to be afew 1013cm-2 in the gas seen in emission, and }10^{14}$ --1014cm-2 in the components responsible for the absorption, which is indicative of a high line of sight average abundance [CH^+]/[H]> 1.210-8. We show that the CH^+columndensities agree well with the predictions of state-of-the-art C-shockmodels in dense UV-illuminated gas for the emission line, and withthose of turbulent dissipation models in diffuse gas for the absorptionlines.Key words: astrochemistry - ISM: molecules - ISM: kinematics and dynamics - turbulence