| Description |
Among all species detected in the diffuse interstellar medium, CH+ and SH+ are unique. Since their main production pathways are highly endo-energetic, their large observed abundances are likely the signature of the dissipation of turbulence. In addition, since the energies involved in their formation differ by more than a factor of 2, a comparative analysis of CH+ and SH+ provides essential clues on the nature of the dynamical processes involved in turbulent dissipation.We propose here to perform sensitive Herschel/HIFI observations of 13CH+ and SH+ in absorption towards 5 background dust continuum sources located in the inner Galaxy : W49N, G34, W51, DR21(OH), and W33A. Each line-of-sight samples kiloparsecs of diffuse interstellar matter. Given the sensitivity and resolution of HIFI, we propose to reach a signal/noise ratio of about 300 in order to analyze the velocity structure of individual clouds along the sightlines. This project has two main goals : (1) characterize the kinematic signatures of the 13CH+ and SH+ absorption lines and compare them, statistically, to those of molecular species whose formation routes are less (or not) endothermic and (2) confront the 13CH+ and SH+ abundances to model predictions in order to directly derive for the first time the turbulent dissipation rate and the ion-neutral velocity drift driving dissipation in individual diffuse clouds. |
