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Dust-Corrected Star Formation Rates of Galaxies. II. Combinations of Ultraviolet and Infrared Tracers

We present new calibrations of far-ultraviolet (FUV) attenuation as derived from the total infrared to FUV luminosity ratio (IRX) and the FUV-NUV color. We find that the IRX-corrected FUV luminosities are tightly and linearly correlated with the attenuation-corrected Hα luminosities (as measured from the Balmer decrement), with a rms scatter of $\pm 0.09$ dex. The ratios of these attenuation-corrected FUV to Hα luminosities are consistent with evolutionary synthesis model predictions, assuming a constant star formation rate over 100 Myr, solar metallicity and either a Salpeter or a Kroupa IMF with lower and upper mass limits of 0.1 and 100\msun. The IRX-corrected FUV to Balmer-corrected Hα luminosity ratios do not show any trend with other galactic properties over the ranges covered by our sample objects. In contrast, FUV attenuation derived from the FUV-NUV color (UV spectral slope) show much larger random and systematic uncertainties. When compared to either Balmer-corrected Hα luminosities or IRX-corrected FUV luminosities the color-corrected FUV luminosities show $\sim 2.5$ times larger rms scatter, and systematic nonlinear deviations as functions of luminosity and other parameters. Linear combinations of 25um and 1.4GHz radio continuum luminosities with the observed FUV luminosities are also well correlated with the Balmer-corrected Hα luminosities. These results provide useful prescriptions for deriving attenuation-corrected star formation rates of galaxies based on linear combinations of UV and IR or radio luminosities, which are presented in convenient tabular form. Comparisons of our calibrations with attenuation corrections in the literature and with dust attenuation laws are also made.