Modelling the UV to radio SEDs of nearby star-forming galaxies: new Parsec SSP for Grasil

TL;DR

This paper presents an updated stellar population synthesis model combining PARSEC tracks, nebular emission, and radio contributions to accurately predict the spectral energy distributions of star-forming galaxies across UV to radio wavelengths.

Contribution

The authors develop a comprehensive panchromatic SED model for star-forming galaxies incorporating new stellar tracks, nebular emission, and radio components, with calibration tools for various galaxy properties.

Findings

Model accurately fits observed galaxy SEDs

Provides SFR calibrations from UV to radio wavelengths

Constrains IMF upper mass limit using multi-wavelength data

Abstract

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.