Nebular Continuum and Line Emission in Stellar Population Synthesis Models

TL;DR

This paper introduces a new nebular emission model integrated into stellar population synthesis, enhancing the accuracy of galaxy spectral energy distribution modeling by coupling nebular emission with stellar spectra.

Contribution

The paper presents a self-consistent nebular emission model within the Flexible Stellar Population Synthesis code that accurately scales emission line intensities with stellar population properties.

Findings

Model agrees with other photoionization models and observations.

Reproduces emission from H II regions and star-forming galaxies.

Shows improved agreement with observed emission line ratios.

Abstract

Accounting for nebular emission when modeling galaxy spectral energy distributions (SEDs) is important, as both line and continuum emission can contribute significantly to the total observed flux. In this work, we present a new nebular emission model integrated within the Flexible Stellar Population Synthesis code that computes the total line and continuum emission for complex stellar populations using the photoionization code Cloudy. The self-consistent coupling of the nebular emission to the matched ionizing spectrum produces emission line intensities that correctly scale with the stellar population as a function of age and metallicity. This more complete model of galaxy SEDs will improve estimates of global gas properties derived with diagnostic diagrams, star formation rates based on H$\alpha$, and stellar masses derived from NIR broadband photometry. Our models agree well with results from other photoionization models and are able to reproduce observed emission from H II regions and star-forming galaxies. Our models show improved agreement with the observed H II regions in the Ne III/O II plane and show satisfactory agreement with He II emission from $z=2$ galaxies when including rotating stellar models. Models including post-asymptotic giant branch stars are able to reproduce line ratios consistent with low-ionization emission regions (LIERs).