Predicted α_CO conversion factors (open triangles) by the functional form derived in Narayanan et al. (2012) in the case of solar gas-phase metallicity and compact (radius of 5 kpc; red), or extended (radius of 25 kpc; black) molecular gas distributions, as a function of CO surface brightness given by the ratio between and the molecular gas surface. We also show the value adopted in this work (α_CO = 3.5 M_⊙ pc⁻² (K km s⁻¹)⁻¹; horizontal solid green line), and the predicted value derived from the empirical relation derived by Amorín et al. (2016) assuming solar metallicity (α_CO = 4.8 M_⊙ pc⁻² (K km s⁻¹)⁻¹; horizontal dotted blue line).