SFR-Hα luminosity relations of the canonical invariant IMF and the IGIMF-2021 theory. Left panel: Star formation rate in dependence of the Hα luminosity assuming a canonical IMF (solid black line; Kennicutt 1998) and the IGIMF-2021 theory (coloured lines) for different metallicities [Z] shown on the right colorbar. The Hα fluxes are calculated with the PÉGASE code (see text). Right panel: Conversion factor of the SFRs, $\mathrm{\Phi }=\frac{{\psi }_{\mathrm{IGIMF}}}{{\psi }_{\mathrm{K}98}}$, in dependence of the Hα luminosity. The solid black line refers to ψ_IGIMF = ψ_K98. The fitting parameters are listed in Table B.1.