Simulated [C II] LF compared with observational estimates. The coloured lines represent the best-fit DPL – Eq. (2) – to the simulated LF and the shaded area represents the central 68% credibility range obtained using the MCMC chains. Black stars represent the observational estimates at z ∼ 4.5 from the ALPINE survey (Yan et al. 2020) and the grey arrow shows the lower limit from Swinbank et al. (2012) based on observations of two galaxies at z ∼ 4.4. The dashed and dotted horizontal lines represent a number count of 1 per dex in the entire simulation volume of M25 and M50, respectively. The [C II] LF from Popping et al. (2016) and Lagache et al. (2018) both based on a semi-analytical galaxy formation model, and from Garcia et al. (2024) obtained by post-processing the SIMBA simulations at z = 6 and 5 are included in the respective panels.