Abstract We present radial profiles of surface brightness in UV and IR bands, estimate stellar mass surface density (Ξ£ β ) and star formation rate surface density (Ξ£ SFR ), and predict the CO-to-H 2 conversion factor ( Ξ± CO ) for over 5000 local galaxies with stellar mass M β β₯ 10 9.3 M β . We build these profiles and measure galaxy half-light radii using GALEX and WISE images from the z 0MGS program, with special care given to highly inclined galaxies. From the UV and IR surface brightness profiles, we estimate Ξ£ β and Ξ£ SFR and use them to predict Ξ± CO with state-of-the-art empirical prescriptions. We validate our (kpc-scale) Ξ± 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 Ξ± CO to observed galaxy-integrated SFR to CO luminosity ratio as a function of M β . A large compilation of literature data suggests that star-forming galaxies with M β = 10 9.5β11 M β show strong anticorrelations of SFR/ L β² CO ( 1 β 0 ) β M β β 0.29 and SFR/ L β² CO ( 2 β 1 ) β M β β 0.40 . The estimated Ξ± CO trends, when combined with a constant molecular gas depletion time t dep , can only explain β1/3 of these SFR/ L β² 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 β² CO variations. We publish all data products from this work, including galaxy sizes, UV and IR surface brightness profiles, Ξ£ β , Ξ£ SFR , and Ξ± CO estimates.
Chiang et al. (Fri,) studied this question.
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