We examine what types of galaxies the conversion formula from dust infrared ( IR ) luminosity into the star formation rate ( SFR ) derived by Kennicutt ( 1998 ) is applicable to .
The ratio of the observed IR luminosity , L _ { IR } , to the intrinsic bolometric luminosity of the newly ( \lesssim 10 Myr ) formed stars , L _ { SF } , of a galaxy can be determined by a mean dust opacity in the interstellar medium and the activity of the current star formation .
We find that these parameters area being 0.5 \leq L _ { IR } / L _ { SF } \leq 2.0 is very large , and many nearby normal and active star-forming galaxies really fall in this area .
It results from offsetting two effects of a small dust opacity and a large cirrus contribution of normal galaxies relative to starburst galaxies on the conversion of the stellar emission into the dust IR emission .
In conclusion , the SFR determined from the IR luminosity under the assumption of L _ { IR } = L _ { SF } like Kennicutt ( 1998 ) is reliable within a factor of 2 for all galaxies except for dust rich but quiescent galaxies and extremely dust poor galaxies .