Modelling the nebular emission from primeval to present-day star-forming galaxies

Abstract

We present a new model of the nebular emission from star-forming galaxies in a wide range of chemical compositions, appropriate to interpret observations of galaxies at all cosmic epochs. The model relies on the combination of state-of-the-art stellar population synthesis and photoionization codes to describe the ensemble of H ii regions and the diffuse gas ionized by young stars in a galaxy. A main feature of this model is the self-consistent yet versatile treatment of element abundances and depletion onto dust grains, which allows one to relate the observed nebular emission from a galaxy to both gas-phase and dust-phase metal enrichment. We show that this model can account for the rest-frame ultraviolet and optical emission-line properties of galaxies at different redshifts and find that ultraviolet emission lines are more sensitive than optical ones to parameters such as C/O abundance ratio, hydrogen gas density, dustto-metal mass ratio and upper cutoff of the stellar initial mass function. We also find that, for gas-phase metallicities around solar to slightly sub-solar, widely used formulae to constrain oxygen ionic fractions and the C/O ratio from ultraviolet and optical emission-line luminosities are reasonable faithful. However, the recipes break down at non-solar metallicities, making them inappropriate to study chemically young galaxies. In such cases, a fully self-consistent model of the kind presented in this paper is required to interpret the observed nebular emission.

Biases in Metallicity Measurements from Global Galaxy Spectra: The Effects of Flux Weighting and Diffuse Ionized Gas Contamination

“…For photoionization models, it is difficult to determine the proper combination of input parameters and physical conditions that produce realistic H ii regions because of degeneracies among parameters. Additionally, observed nearby H ii regions often have filamentary gas structures and cluster stars distributed throughout the ionized gas (e.g., 30 Dor; Pellegrini et al 2011), a very different geometry from the ionizing point source and uniform-density sphere or slab of gas utilized in most photoionization codes (Kewley & Dopita 2002;Gutkin et al 2016).…”

Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances*

“…We used the large grid of photoionization models described in Feltre et al (2016) and Gutkin et al (2016) to investigate the nature of the ionizing source. In all the diagnostic diagrams, ID14 belongs to the regions powered by star formation (e.g., see Figure 8).…”

“…Diagnostic diagram separating AGN and star-forming powered sources with superimposed object ID14 and a similar object described in Vanzella et al (2016a). Predictions are from photoionization models of Feltre et al (2016; AGNs, gray-filled circles) and Gutkin et al (2016). Star-forming galaxies are color-coded according to their gas phase metallicity, Z gas , as defined in Gutkin et al (2016).…”

“…Predictions are from photoionization models of Feltre et al (2016; AGNs, gray-filled circles) and Gutkin et al (2016). Star-forming galaxies are color-coded according to their gas phase metallicity, Z gas , as defined in Gutkin et al (2016).…”

Ultraviolet/Optical Emission of the Ionized Gas in AGN: Diagnostics of the Ionizing Source and Gas Properties

“…We also consider new generation photoionization calculations of the nebular emission from stars , parametrized in analogous way to the AGN NLR models. We remind the reader to the papers of Charlot and Longhetti (2001), Gutkin et al (2016) for a detailed description of these spectral models. Hα and Hβ) are commonly used to distinguish between stellar and nuclear activity (e.g., Baldwin et al, 1981;Veilleux and Osterbrock, 1987).…”