Modeling the UV to Radio Spectral Energy Distribution of NGC 6946: Star Formation Rates and Dust Attenuation Properties

Abstract In this paper, we perform an ultraviolet (UV) to radio spectral energy distribution fitting analysis of star-forming regions in the nearby galaxy NGC 6946 by means of the Graphite and Silicates ( GRASIL ) population synthesis and radiative transfer model to which the first version of the thoroughly updated Padova and Trieste Stellar Evolutionary Code (PARSEC v1.2s) database of evolutionary nonrotating tracks of massive stars is incorporated. The tracks span a wide range of initial chemical compositions ( Z = 0.0001–0.04) and stellar initial mass function (IMF) upper mass limits ( M up = 40 M ⊙ –350 M ⊙ ). We obtain from our best-fit models consistent and robust estimates of star formation rate calibrations at wavelengths ranging from UV to radio and as a function of IMF upper mass limit. We investigate the properties of dust attenuation curves that also result from the best-fit models by exploiting the realistic treatment of dust performed by GRASIL . This resulted in new relations between optical emission fluxes that are subject to attenuation and fluxes that are not prone to attenuation. These relations, which we show to be almost independent of IMF upper mass limits, can be extremely useful in estimating attenuations in young high redshift galaxies.