Modelling the UV to radio SEDs of nearby star-forming galaxies: new
  Parsec SSP for Grasil
  By means of the updated PARSEC database of evolutionary tracks of massive
stars, we compute the integrated stellar light, the ionizing photon budget and
the supernova rates of young simple stellar populations (SSPs), for different
metallicities and IMF upper mass limits. Using CLOUDY we compute and include in
the SSP spectra the neb- ular emission contribution. We also revisit the
thermal and non-thermal radio emission contribution from young stars. Using
GRASIL we can thus predict the panchromatic spectrum and the main recombination
lines of any type of star-forming galaxy, including the effects of dust
absorption and re-emission. We check the new models against the spectral energy
distributions (SEDs) of selected well-observed nearby galaxies. From the
best-fit models we obtain a consistent set of star formation rate (SFR)
calibrations at wavelengths ranging from ultraviolet (UV) to radio. We also
provide analytical calibrations that take into account the dependence on
metallcity and IMF upper mass limit of the SSPs. We show that the latter limit
can be well constrained by combining information from the observed far
infrared, 24 {\mu}m, 33 GHz and H{\alpha} luminosities. Another interesting
property derived from the fits is that, while in a normal galaxy the
attenuation in the lines is significantly higher than that in the nearby
continuum, in individual star bursting regions they are similar, supporting the
notion that this effect is due to an age selective extinction. Since in these
conditions the Balmer decrement method may not be accurate, we provide
relations to estimate the attenuation from the observed 24 {\mu}m or 33 GHz
fluxes. These relations can be useful for the analysis of young high redshift
galaxies.
