The units of the x-axis are normalized to the position of the shock front.
Ionizing radiation comes from the left.
This means that the structure is stretched along the x-axis with time. The convergence of the code toward the correct solution with increasing resolution can be tested in one calculation, since for all structures the ratio between structure sizes and smoothing lengths increases linearly with time. Note that here the case of a weak D-type ionization front is realized. The resolution of 192 grid cells along the slab of their calculations, from which they derived their results, is comparable with the one used in our high resolution case. We use the same method as described in Sect.