Scatter Δ around the FP for different sources data and different definitios of Δ. Left panel: scatter around the FP for Illutris-1 (upper panel) and IllustrisTNG-100 (lower panel) obtained from simulations. The dots of different colors mark the values of the scatter obtained for different range of masses: red dots (log(M_s/M_⊙) > 11), blue dots (log(M_s/M_⊙) > 10), green dots (log(M_s/M_⊙) > 9), black dots (log(M_s/M_⊙) > 8), magenta dots (log(M_/ M_⊙) > 7). The colored lines give the average scatter across time for each mass sample. The Δ’s are calculated according Eq. (5). Right panel: scatter around the FP for Illustris-1 (red dots) and IllustrisTNG-100 (blue dots) at different redshift. In this case the scatter is obtained from the difference of the measured log(R_e) and the value calculated using the expression of the FP with fixed coefficients given by the sample at z = 0 with masses larger than 10¹⁰ M_⊙. The Δ’s are calculated according Eq. (7). The upper and lower panels show the scatter for the two samples of models with different low mass limit.