The various X_CO Galactic radial profiles available in the literature are displayed in the left panel. The corresponding variations in the γ-ray flux at 30 GeV and b = 0° are displayed relative to our reference model of Fig. 1 for which the constant value of 2.3 × 10²⁰ molecules cm^-2 (K km s^-1)^-1 has been assumed for X_CO. The three (cyan) peaks, whose maxima have not been displayed for clarity, reach a value of 3.0, 2.3, and 2.3 respectively from left to right.