Distribution of IllustrisTNG galaxies across the sSFR₉ versus sSFR₈ plane. Left and right columns show the distribution based on the true (null values of sSFR are arbitrarily set to log₁₀(sSFR/yr⁻¹) = −15) and inferred median values, respectively. Top row panels display the full sample RGB colour-coded by the probability of belonging to the retired, quenched, and ageing classes. Solid and dotted lines represent the demarcation lines given by Eqs. (2) and (3), respectively. Middle and bottom rows illustrate the two proposed approaches for selecting quenched galaxies (coloured points) by colouring in black with low transparency those systems classified as retired or ageing.