Correlations between IR Luminosity, Star Formation Rate, and CO Luminosity in the Local Universe

Abstract: We exploit the DustPedia sample of galaxies within approximately 40 Mpc, selecting 388 sources, to investigate the correlations between IR luminosity (L${\rm IR}$), the star formation rate (SFR), and the CO(1-0) luminosity (L${\rm CO}$) down to much lower luminosities than reached by previous analyses. We find a sub-linear dependence of the SFR on L${\rm IR}$. Below $\log(\hbox{L}{\rm IR}/\hbox{L}\odot)\simeq 10$ or $\hbox{SFR}\simeq 1\,\hbox{M}\odot\,\hbox{yr}^{-1}$, the SFR/L${\rm IR}$ ratio substantially exceeds the standard ratio for dust-enshrouded star formation, and the difference increases with decreasing L${\rm IR}$ values. This implies that the effect of unobscured star formation overcomes that of dust heating by old stars, at variance with results based on the $\textit{Planck}$ ERCSC galaxy sample. We also find that the relations between the L${\rm CO}$ and L${\rm IR}$ or the SFR are consistent with those obtained at much higher luminosities.