Mass-dependent SFH of bulges and resulting evolution of δ_io for a galaxy downsizing scenario. Upper panel: SFR parameterizations simulating a downsizing trend for galaxy bulges by assuming that their age at the peak of their SFR and their SF e-folding timescale inversely with ℳ_⋆. High-, intermediate-, and low-mass bulges (iC, iB, and iA, respectively, in the classification by BP18) reach their maximum SFR at 0.47, 1.2, and 2.4 Gyr. Lower panel: evolution of δ_io (approximated by 2.5 ⋅ log(ψ), as in Fig. 2) in the B and R band (solid and dashed curves, respectively) for the three SFH scenarios for the bulge (upper panel) when a constant SFR for the outer disk is assumed. The shaded gray area depicts the redshift interval 0.76 ≤ z ≤ 2.3 that will be covered both by the MOONS spectrograph at VLT (0.65–1.8 μm) and the B-band filter (∼0.37–0.54 μm). The amplitude of δ_io at z ∼ 1 (vertical white line) depends on galaxy mass. It is moderate (∼0.85 B mag) for low-mass (< L^⋆) galaxies and reaches ∼2 mag for massive LTGs in advanced stages of SF quenching.