Filling factor in the H ii region of hot gas above the threshold temperatures indicated in the legend, as a function of time. Panel a) is for simulation V16, b) for V08, c) for V06, and d) for V04. The H ii region leaves the simulation domain downstream for simulations V16 and V08 at a time indicated with the vertical lines in panels a) and b). All photoionized gas in the H ii region that has not been shock-heated has 5000 K ≤ T ≤ 10 000 K.