Conversion Law of Infrared Luminosity to Star-Formation Rate for Galaxies

We construct a new algorithm for estimating the star formation rate (SFR) ofgalaxies from their infrared (IR) luminosity by developing the theory of the IRemission from a dusty H II region. The derived formula is ${\rm SFR}/(\MO {\rm yr^{-1}})=\{3.3\times10^{-10}(1-\eta)/ (0.4-0.2f+0.6 \epsilon)\}(L{\rm ^{obs}_{IR}}/\LO)$, where $f$ is the fractionof ionizing photons absorbed by hydrogen, $\epsilon$ is the efficiency of dust absorption for nonionizing photons fromOB stars, and $\eta$ is the cirrus fraction of observed IR luminosity. The previous conversion formulae of SFR from the IR luminosity is applicableto only the case where the observed IR luminosity is nearly equal to thebolometric luminosity (starburst galaxies etc.), except for some empiricalformulae. On the other hand, our theoretical SFR is applicable to galaxies even with amoderate star formation activity. That is, our simple and convenient formula is significantly useful forestimating the SFR of various morphologies and types of galaxies --- from earlyelliptical to late spiral and irregular galaxies, or from active starburst toquiescent galaxies --- as far as they have neither an abnormal dust-to-gasratio nor an evident active galactic nucleus.Comment: 5 pages, no figure, accepted by PAS