Comparison of fiducial IllustrisTNG simulation with observational trends. From top to bottom: stellar half-mass radius, R_*, 1/2, DM fraction within R_*, 1/2, f_DM, and DM mass within R_*, 1/2, M_DM, 1/2, as a function of stellar mass, M_*, for the fiducial IllustrisTNG simulation 1P_1_0, compared with the corresponding SPIDER (black curves), ATLAS^3D (dark red curves) and MaNGA DynPop (orange curves) trends. The shaded areas represent the scatter of the observed relations, given by the difference between the 16th and the 84th percentiles with the median. As an example, the open circles are galaxies not used for the evaluation of the cumulative reduced chi-squared associated to the ATLAS^3D observational trend in Section 4.2.