Distribution of central galaxies at z = 0 as a function of SFR and M_*, for SIMBA and TNG in 100 Mpc/h, from left to right, respectively. The coloured background is the logarithmic number of central galaxies. The black dot-dashed line is the SFMS of TNG100, following the definition in Ma et al. (2022): log(SFR/yr⁻¹ M_⊙) = 0.83log M_* − 8.32, and black cross represents SFMS of star-forming central galaxies in SIMBA100, where star-forming galaxies are simply selected with log(sSFR/Gyr⁻¹ M_⊙)≥ − 1.8. Magenta lines separate the star-forming and quenched galaxies in both panels.