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We measure the CO-to-H$_2$ conversion factor ($\alpha_\mathrm{CO}$) in 37galaxies at 2~kpc resolution, using dust surface density inferred fromfar-infrared emission as a tracer of the gas surface density and assuming aconstant dust-to-metals ratio. In total, we have $\sim790$ and $\sim610$independent measurements of $\alpha_\mathrm{CO}$ for CO (2-1) and (1-0),respectively. The mean values for $\alpha_\mathrm{CO~(2-1)}$ and$\alpha_\mathrm{CO~(1-0)}$ are $9.3^{+4.6}_{-5.4}$ and$4.2^{+1.9}_{-2.0}~M_\odot~pc^{-2}~(K~km~s^{-1})^{-1}$, respectively. TheCO-intensity-weighted mean for $\alpha_\mathrm{CO~(2-1)}$ is 5.69, and 3.33 for$\alpha_\mathrm{CO~(1-0)}$. We examine how $\alpha_\mathrm{CO}$ scales withseveral physical quantities, e.g.\ star-formation rate (SFR), stellar mass, anddust-mass-weighted average interstellar radiation field strength($\overline{U}$). Among them, $\overline{U}$, $\Sigma_{\rm SFR}$, andintegrated CO intensity ($W_\mathrm{CO}$) have the strongest anti-correlationwith spatially resolved $\alpha_\mathrm{CO}$. We provide linear regressionresults to \aco for all quantities tested. At galaxy integrated scales, weobserve significant correlations between $\alpha_\mathrm{CO}$ and$W_\mathrm{CO}$, metallicity, $\overline{U}$, and $\Sigma_{\rm SFR}$. We alsofind that the normalized $\alpha_\mathrm{CO}$ decreases with stellar masssurface density ($\Sigma_\star$) in the high surface density regions($\Sigma_\star\geq100~{\rm M_\odot~pc^{-2}}$), following the power-lawrelations $\alpha_\mathrm{CO~(2-1)}\propto\Sigma_\star^{-0.5}$ and$\alpha_\mathrm{CO~(1-0)}\propto\Sigma_\star^{-0.2}$. The power-law index isinsensitive to the assumed dust-to-metals ratio. (abridged)

Resolved Measurements of the CO-to-H$_2$ Conversion Factor in 37 Nearby Galaxies