Panel a: fraction of cells inside the mesh where the optical depth is being limited as a function of time (red solid line). The dashed black line shows the density at the centre of the system as a function of time. Panel b: number of cells in each level (grey) and the number of cells where the optical depth floor is operating (red), at a time of 28.180 kyr, when the first Larson core is formed. Panel c: relative difference in 2D histograms of gas temperature as a function of density for all the cells in a simulation with optical depth limitation and a second simulation without, at t = 28.180 kyr. The colour scale gives a measure of ℛ = N_limited/N_{not limited} − 1, where N_… is the number of cells binned inside a (ρ, T) pixel for the two different simulations. Panel d: same as panel c but in the case of the Rosseland mean opacity as a function of density.