2025ApJ...994..263S

We present radial profiles of surface brightness in UV and IR bands, estimate stellar mass surface density (Σ_⋆) and star formation rate surface density (Σ_SFR), and predict the CO-to-H₂ conversion factor (α_CO) for over 5000 local galaxies with stellar mass M_⋆ ≥ 10^9.3M_⊙. We build these profiles and measure galaxy half-light radii using GALEX and WISE images from the z0MGS program, with special care given to highly inclined galaxies. From the UV and IR surface brightness profiles, we estimate Σ_⋆ and Σ_SFR and use them to predict α_CO with state-of-the-art empirical prescriptions. We validate our (kpc-scale) α_CO predictions against observational estimates, finding the best agreement when accounting for CO-dark gas as well as CO emissivity and excitation effects. The CO-dark correction plays a primary role in lower-mass galaxies, whereas CO emissivity and excitation effects become more important in higher-mass and more actively star-forming galaxies, respectively. We compare our estimated α_CO to observed galaxy-integrated SFR to CO luminosity ratio as a function of M_⋆. A large compilation of literature data suggests that star-forming galaxies with M_⋆ = 10^9.5–11M_⊙ show strong anticorrelations of SFR/$L{{\prime} }_{{\rm{CO}}(1\,\unicode{x02013}\,0)}\propto {M}_{\star }^{-0.29}$ and SFR/$L{{\prime} }_{{\rm{CO}}(2\,\unicode{x02013}\,1)}\propto {M}_{\star }^{-0.40}$. The estimated α_CO trends, when combined with a constant molecular gas depletion time t_dep, can only explain ≈1/3 of these SFR/$L{{\prime} }_{{\rm{CO}}}$ trends. This suggests that t_dep being systematically shorter in lower-mass star-forming galaxies is the main cause of the observed SFR/$L{{\prime} }_{{\rm{CO}}}$ variations. We publish all data products from this work, including galaxy sizes, UV and IR surface brightness profiles, Σ_⋆, Σ_SFR, and α_CO estimates.