Mapping the large scale CO-depletion in the IRDC G351.77-0.51

Abstract

Knowledge of the degree of CO-depletion provides information on the physical conditions occurring in the innermost and the densest regions of molecular clouds. A key parameter is the radius within which the CO is depleted (R_dep). We present a study of the depletion of CO in the Infrared Dark Cloud G351.77-0.51 (G351), to derive the depletion across the cloud. We use the Herschel (Hi-Gal) and LABOCA dust continuum data, combined with APEX C18O and C17O(2-1) line observations. We built a simple model to investigate the size of the CO-depleted region in G351. The model suggests that R_dep < 0.15 pc, where we estimate a hydrogen number density > 2× 10^4 cm^-3. These results provide crucial information on the spatial scales on which different chemical processes can operate in high-mass star forming regions.