Rotational diagrams of the CO molecule. The grey line corresponds to a single least-squares fit to the full range of transitions from where a rotational temperature, T_rot, and total gas mass, M_H2, is computed. The characteristic radius of the CO-emitting volume (r_CO) adopted is indicated. The red and blue lines correspond to a two-component model consisting of a “warm” and “hot” region, respectively. Asterisks indicate line blends that were excluded in the fit.