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

Abstract

We combine H-alpha emission-line and infrared continuum measurements of two\nsamples of nearby galaxies to derive dust attenuation-corrected star formation\nrates (SFRs). We use a simple energy balance based method that has been applied\npreviously to HII regions in the Spitzer Infrared Nearby Galaxies Survey\n(SINGS), and extend the methodology to integrated measurements of galaxies. We\nfind that our composite H-alpha+IR based SFRs are in excellent agreement with\nattenuation-corrected SFRs derived from integrated spectrophotometry, over the\nfull range of SFRs (0.01 -- 80 solar mass per year) and attenuations (0 -- 2.5\nmag) studied. We find that the combination of H-alpha and total infrared\nluminosities provides the most robust SFR measurements, but combinations of\nH-alpha measurements with monochromatic luminosities at 24 micron and 8 micron\nperform nearly as well. The calibrations differ significantly from those\nobtained for HII regions (Calzetti et al. 2007), with the difference\nattributable to a more evolved population of stars heating the dust. Our\nresults are consistent with a significant component of diffuse dust (the `IR\ncirrus' component) that is heated by a non-star-forming population. The same\nmethodology can be applied to [OII]$\\lambda$3727 emission-line measurements,\nand the radio continuum fluxes of galaxies can be applied in place of IR fluxes\nwhen the latter are not available. We assess the precision and systematic\nreliability of all of these composite methods.\n