Left: halo mass function (HMF) of the 979 galaxies identified inside FIREbox within the mass range 10 ≤ log(M_vir/M_⊙) ≤ 14 (red). Vertical dashed lines show the range of the virial masses used for halo identification. Grey arrows indicate the re-weighting operated to match the HMF in FIREbox with a ‘universal’ HMF extracted from dark matter cosmological simulation (in black line, from Tinker et al. 2008). Right: galaxy stellar mass function (GSMF) for this same set of galaxies identified inside FIREbox (red), and with each galaxy re-weighted with the operation presented in the left-hand panel (orange). Two examples of GSMF built on observations of galaxies in the local Universe are also shown. The black solid line is the best-fit GSMF at z ~ 0.1 from Tomczak et al. (2014) and the dashed line is the median GSMF generated using the continuity model parameters of Leja et al. (2020) at z = 0. The shaded grey area corresponds to the 16–84% uncertainties associated with this model.