Galaxy stellar mass–size relation of simulations analysed in this paper: (from left to right) TNG100, EAGLE, and TNG50. We chose the stellar mass, M_*, defined within a spherical radius of 30 kpc vs. r₅₀ defined from a 2D image. The galaxies kept in our analysis with M_* > 10^10.3 M_⊙ are coloured in blue, the galaxies with ongoing mergers are removed from our analysis and are coloured in grey.