Stellar Population Synthesis (SPS) is a key ingredient in forward models for galaxy emission (see Conroy 2013).
I have used SPS models in a wide range of projects. Most recently, Sophie Newman, a student at the ICG, used the CLOUDY photoionization code to explore the line and continuum emission properties of young star forming regions (Newman et al., 2025), utilising our Synthesizer code.
Stellar, nebular line and continuum emission components from the M24 Maraston models
(Newman et al., 2025).
I have also developed an online tool, Sengi, for exploring SPS models in an interactive way. Details on the implementation are published in (Lovell, 2021).
References
2025
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Cloudy-Maraston: Integrating nebular continuum and line emission with the Maraston stellar population synthesis models
Sophie L. Newman, Christopher C. Lovell, Claudia Maraston, and 5 more authors
Jan 2025
arXiv:2501.03133 [astro-ph]
The James Webb Space Telescope has ushered in an era of abundant high-redshift observations of young stellar populations characterized by strong emission lines, motivating us to integrate nebular emission into the new Maraston stellar population model which incorporates the latest Geneva stellar evolutionary tracks for massive stars with rotation. We use the photoionization code Cloudy to obtain the emergent nebular continuum and line emission for a range of modelling parameters, then compare our results to observations on various emission line diagnostic diagrams. We carry out a detailed comparison with several other models in the literature assuming different input physics, including modified prescriptions for stellar evolution and the inclusion of binary stars, and find close agreement in the H{}rm }beta H{}rm }alpha [N II]{}lambda 6583 and [S II]{}lambda 6731 luminosities between the models. However, we find significant differences in lines with high ionization energies, such as He II{}lambda\1640 and [O III]{}lambda 5007 due to large variations in the hard ionizing photon production rates. The models differ by a maximum of {}hat{Q}_{}rm [O III]}lambda 5007} = }rm 6 }times 10^9 }; s^{-1} }, M_{}odot}^{-1} where these differences are mostly caused by the assumed stellar rotation and effective temperatures for the Wolf Rayet phase. Interestingly, rotation and uncorrected effective temperatures in our single star population models alone generate [O III] ionizing photon production rates higher than models including binary stars with ages between 1 to 8 Myr. These differences highlight the dependence of derived properties from SED fitting on the assumed model, as well as the sensitivity of predictions from cosmological simulations.
2021
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Sengi: A small, fast, interactive viewer for spectral outputs from stellar population synthesis models
C. C. Lovell
A&C, Jan 2021
We present Sengi, (https://christopherlovell.github.io/sengi), an online tool for viewing the spectral outputs of stellar population synthesis (SPS) codes. Typical SPS codes require significant disk space or computing resources to produce spectra for simple stellar populations with arbitrary parameters. This makes it difficult to present their results in an interactive, web-friendly format. Sengi uses Non-negative Matrix Factorisation (NMF) and bilinear interpolation to estimate output spectra for arbitrary values of stellar age and metallicity. The reduced disk requirements and computational expense allows the result to be served as a client-based Javascript application. In this paper we present the method for generating grids of spectra, fitting those grids with NMF, bilinear interpolation across the fitted coefficients, and finally provide estimates of the prediction and interpolation errors.