Fig. 1. The confidence regions for individual galaxies in the parameter space within which 90 percent of the total posterior probability is found

Fig. 2. The 90 percent confidence region of the joint likelihood for all galaxies and how it depends on the CO-H₂ conversion factor X. The solid line refers to the standard value X=3.68, short dashes indicate X/3.68 = 0.1 and 100, and long dashes are done with the metallicity-dependent prescription of Arimoto et al. (1996)

Fig. 3. The ratios of Halpha surface brightness and surface density g of the total gas as a function of the local gas fraction f_gas in the Milky Way. The black dot indicates the inner 3 kpc

Fig. 4. The gas fraction as a function of galactocentric distance

Fig. 5. Contours of the joint probability density for all galaxies of models which accrete gas decreasing exponentially in time and allow radial inflow of gas. The density varies by a factor 100 between contour lines. That the confidence region is divided in two islands is due to the coarseness of the integration grids