Chemical Evolution and Far-Infrared Emission of Galaxies

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Infrared (IR) dust emission from galaxies is frequently used as an indicator of starformation rate (SFR). However, the effect of dust-to-gas ratio, or amount of dust, on the con-version law from IR luminosity to SFR has not been considered. In this paper, we present aconvenient formula including the effect. In order to obtain the dependence of the dust-to-gasratio, we extend the formula derived in our previous paper, in which a theoretical formula con-verting IR luminosity to SFR was derived. That formula was expressed as SFR=(M yr-1) ={3.3 ×10-10(1-η)/(0.4 - 0.2f + 0.6ε)}(LIR=L), where f is the fraction of ionizing photons ab-sorbed by hydrogen, εis the effciency of dust absorption for nonionizing photons, ηis the cirrusfraction of observed dust luminosity, and LIR is the observed luminosity of dust emission in the8-1000-μm range. Throughout the current discussion, we construct an algorithm to relate f andε, both of which depend on the dust-to-gas ratio, to the metallicity, by adopting a galactic relationbetween dust-to-gas ratio and metallicity. Thus, we estimate the metallicity dependence of ourformula. We apply the result to the cosmic star formation history and find that the comoving SFRat z 〜 3 calculated from previous empirical formulae is underestimated by the factor of 4. Finally,we comment on the HII/L2 mission (SPICA).
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