DUST-CORRECTED STAR FORMATION RATES OF GALAXIES. I. COMBINATIONS OF Hα AND INFRARED TRACERS

We combine H alpha emission-line and infrared (IR) continuum measurements of two samples of nearby galaxies to derive dust attenuation-corrected star formation rates (SFRs). We use a simple energy balance based method that has been applied previously to H II regions in the Spitzer Infrared Nearby Galaxies Survey, and extend the methodology to integrated measurements of galaxies. We find that our composite H alpha + IR based SFRs are in excellent agreement with attenuation-corrected SFRs derived from integrated spectrophotometry, over the full range of SFRs (0.01-80 M-circle dot yr(-1)) and attenuations (0-2.5 mag) studied. We find that the combination of H alpha and total IR luminosities provides the most robust SFR measurements, but combinations of H alpha measurements with monochromatic luminosities at 24 mu m and 8 mu m perform nearly as well. The calibrations differ significantly from those obtained for H II regions, with the difference attributable to a more evolved population of stars heating the dust. Our results are consistent with a significant component of diffuse dust (the IR cirrus component) that is heated by a non-star-forming population. The same methodology can be applied to [O II]lambda 3727 emissionline measurements, and the radio continuum fluxes of galaxies can be applied in place of IR fluxes when the latter are not available. We assess the precision and systematic reliability of all of these composite methods.