Time evolution of M_g vs M_star over the last 50% of the galaxies’ lifetime, according to the toy-model based on three exponential SFHs: β = ( − 1, 0, 1), and also assuming that the SFR timescale τ_SF is the same as the gas depletion time, τ_g = . Galaxy age t_gal is given by Eq. (B.4), ψ₀ by Eq. (B.3), and the M_g evolution by Eq. (14). The median curves in different M_star bins are plotted, where the (median observed) gas mass M_g is taken to be M_g(t_gal). For Δη = α, the equilibrium solution, M_g = M_i throughout the lifetime of the galaxy.