Modelling emission lines in star-forming galaxies. Issue 2 (3rd December 2021)

• Record Type: Journal Article
• Authors: Baugh, C M; Lacey, Cedric G; Gonzalez-Perez, Violeta; Manzoni, Giorgio
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 510:Issue 2(2022)
• Page Start: 1880
• Page End: 1893
• Publication Date: 2021-12-03
• Subjects: methods: numerical -- H ii regions -- galaxies: formation; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab3506
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: 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.