Main panel: the evolution of the M_BH (bottom) of galaxies with σ > 100 km s⁻¹ in Illustris. Red shows the galaxies with overmassive SMBHs and blue shows galaxies with undermassive SMBHs. Faint lines show the trajectory of individual galaxies. Thick dashed lines connect the median values of the two populations at each lookback time. The dips (downward trend followed by a sudden increase) represent a misidentification of the main progenitor, which can occur during mergers (Rodriguez-Gomez et al. 2015). The small panel on the left shows the distribution of M_BH at z = 0. Again, red shows the galaxies with overmassive SMBHs and blue shows galaxies with undermassive SMBHs. The black line shows the mass distribution of all the SMBHs in galaxies with σ > 100 km s⁻¹ in Illustris.