Conversion law of infrared luminosity to star-formation rate for galaxies

We construct a new algorithm for estimating the star-formation rate (SFR) o f galaxies from their infrared (IR) luminosity by developing the theory of the IR emission from a dusty H II region. The derived formula is SFR/(M-cir cle dot, yr(-1)) = [3.3 x 10(-10)(1 -eta)/(0.4 - 0.2f + 0.6 epsilon)](L-IR( obs)/L-circle dot), where f is the fraction of ionizing photons absorbed by hydrogen, epsilon is the efficiency of dust absorption for nonionizing pho tons from OB stars, and eta is the cirrus fraction of observed IR luminosit y. The previous conversion formulae of SFR from the IR luminosity are appli cable to only the case where the observed IR luminosity is nearly equal to the bolometric luminosity (starburst galaxies etc.), except for some empiri cal formulae. On the other hand, our theoretical SFR is applicable to galax ies even with a moderate star-formation activity. That is, our simple and c onvenient formula is significantly useful for estimating the SFR of various morphologies and types of galaxies - from early elliptical to late spiral and irregular galaxies, or from active starburst to quiescent galaxies - as long as they have neither an abnormal dust-to-gas ratio nor an evident act ive galactic nucleus.