On the conversion of carbon monoxide intensities to molecular hydrogen abundances

The study of interstellar molecular clouds involves frequently the problem of a determination of the molecular hydrogen (H2) content of various clouds. However, H2 is generally not observable from the ground. For this reason, information on H2 is commonly obtained on the basis of an observation of trace molecules, such as carbon monoxide (CO), and a conversion of the CO data into H2 data. Difficulties of such an approach are related to the necessity of an establishment of appropriate conversion factors. To date all studies regarding the CO to H2 conversion are empirical in approach. The present investigation provides results of theoretical cloud modelling with the objective to furnish a basis for guiding empirical decisions on the conversion of CO to H2. A cloud model with known input parameters is used to simulate CO and (C-13)O observations.