Four projections of the FP. The small gray dots mark the observational data. The colored dots are three simulated galaxies (A, B, C) of the Illustris simulation taken along their evolution at z = 4 (blue dots), z = 1 (green dots), and z = 0 (red dots), respectively. The solid lines connect each object in its evolution with time. In this figure < I_e> is equal to I_e and indicate the average effective surface intensity.