Collection of IMFs (normalised to have the same mass). Columns correspond to log₁₀(SFR) = −2, 0 and 2. Each panel shows the number of stars per mass interval: canonical IMF in red and gwIMF in a gradient of greys for each metallicity ([M/H] = −0.4, 0, and 0.22), from lightest to darkest. The vertical blue lines represent the mass of the most massive surviving star when the age of the population is 10, 1, and 0.1 Gyr, corresponding to ≈1.1, 2.3 and 5.4 M_⊙ in each case (assuming solar metallicity). We note that only stars with masses lower than the mass of the most massive surviving star will contribute to the spectra, as the horizontal arrows of the first panel show. The normalisation is performed as explained in Sect. 2.4.