Stellar mass function of the FLAMINGO simulation at z = 0.4. The solid black line represents all the galaxies from the simulation, while the blue and red lines represent the galaxies from the DESI BGS-like and BOSS-like samples. As is explained in Sect. 2.2, the DESI BGS-like sample is complete in M_r with a number density of 10⁻³h³ Mpc⁻³, while the BOSS-like sample is incomplete and red with a number density of 10^−3.5h³ Mpc⁻³.