Infrared (IR) emission from Galactic dust is frequently used as an indicator of the star formation rate (SFR). Recently, A. K. Inoue, H. Hirashita, & H. Kamaya derived a formula for conversion from the IR luminosity to the SFR based on a physical model of H II regions (PASJ, 52, 539, 2000). They expressed this as SFR/(M⊙ yr−1) = {1.1 x 10-10(1-η)/(0.4–0.22f+0.6∊)}(LIR/L⊙), where f is the fraction of ionizing photons absorbed by hydrogen, ∊ is the efficiency of dust absorption for non-ionizing photons, η is the cirrus fraction of the observed dust luminosity, and LIR is the observed luminosity of dust emission. Since f depends on the dust-to-gas ratio and the dust-to-gas ratio is related to metallicity, we present the dependence of the formula on metallicity.

Our metallicity-dependent conversion formula is applied to the cosmic star formation history. Based on a recent model of the cosmic star formation history and metal enrichment history, we find that the photons from OB stars are not efficiently reprocessed in the IR before z ~ 3 because of a low dust-to-gas ratio. This indicates that the star formation rate estimated from the submillimeter luminosity using an empirical formula is significantly underestimated (by at least a factor of 3).