Differences in galaxy colours are not just about the mass Matthee, Jorryt J ; https://orcid.org/0000-0003-2871-127X Astronomy and Astrophysics galaxies formation - galaxies evolution - galaxies star formation - galaxies abundances Observations show that star-forming galaxies reside on a tight three-dimensional plane between mass, gas-phase metallicity and star formation rate (SFR), which can be explained by the interplay between metal-poor gas inflows, SFR and outflows. However, different metals are released on different time-scales, which may affect the slope of this relation. Here, we use central, star-forming galaxies with Mstar = 109.0−10.5 M from the EAGLE hydrodynamical simulation to examine three-dimensional relations between mass, SFR and chemical enrichment using absolute and relative C, N, O and Fe abundances. We show that the scatter is smaller when gas-phase α-enhancement is used rather than metallicity. A similar plane also exists for stellar α-enhancement, implying that present-day specific SFRs are correlated with long time-scale star formation histories. Between z = 0 and 1, the α-enhancement plane is even more insensitive to redshift than the plane using metallicity. However, it evolves at z > 1 due to lagging iron yields. At fixed mass, galaxies with higher SFRs have star formation histories shifted toward late times, are more α-enhanced and this α-enhancement increases with redshift as observed. These findings suggest that relations between physical properties inferred from observations may be affected by systematic variations in α-enhancements. Springer Nature 2021 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/11585 Matthee JJ. Differences in galaxy colours are not just about the mass. <i>Nature Astronomy</i>. 2021;5:984-985. doi:<a href="https://doi.org/10.1038/s41550-021-01415-y">10.1038/s41550-021-01415-y</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1038/s41550-021-01415-y info:eu-repo/semantics/altIdentifier/e-issn/2397-3366 info:eu-repo/semantics/altIdentifier/arxiv/1802.06786 info:eu-repo/semantics/openAccess