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Modelling emission lines in star-forming galaxies

Baugh, CM; Lacey, Cedric G; Gonzalez-Perez, Violeta; Manzoni, Giorgio

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Violeta Gonzalez-Perez

Giorgio Manzoni


We present a new model to compute the luminosity of emission lines in star-forming galaxies and apply this in the semi-analytical galaxy formation code GALFORM. The model combines a pre-computed grid of H II region models with an empirical determination of how the properties of H II regions depend on the macroscopic properties of galaxies based on observations of local galaxies. The new model gives a very good reproduction of the locus of star-forming galaxies on standard line ratio diagnostic diagrams. The new model shows evolution in the locus of star-forming galaxies with redshift on this line ratio diagram, with a good match to the observed line ratios at z = 1.6. The model galaxies at high redshift have gas densities and ionisation parameters that are predicted to be ≈2–3 times higher than in local star-forming galaxies, which is partly driven by the changing selection with redshift to mimic the observational selection. Our results suggest that the observed evolution in emission line ratios requires other H II region properties to evolve with redshift, such as the gas density, and cannot be reproduced by H II model grids that only allow the gas metallicity and ionisation parameter to vary.


Baugh, C., Lacey, C. G., Gonzalez-Perez, V., & Manzoni, G. (2022). Modelling emission lines in star-forming galaxies. Monthly Notices of the Royal Astronomical Society, 510(2), 1880-1893.

Journal Article Type Article
Acceptance Date Nov 25, 2021
Online Publication Date Dec 3, 2021
Publication Date 2022-02
Deposit Date Feb 10, 2022
Publicly Available Date Feb 10, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 510
Issue 2
Pages 1880-1893


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Copyright Statement
© The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society.<br /> This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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