Flux density functions of submillimeter galaxies in the FLAMINGO simulation for z = 0.5 − 6.0 redshift range. The top panel shows prediction using the L21 relation, and the bottom panel displays predictions assuming the H13 relation. The brighter sources increase at a higher rate than the fainter sources from z = 6.0 to z = 2.5, and this is followed by a rapid depletion of bright sources for z < 2.5.