Ionization distribution, high n

Figure 13 shows the ionization and thermal balance of an optically thin photoionized gas analogous to that shown in Figure 8, but at a density of 10$^{17}$ cm$^{-3}$. Comparison shows that the high density results in generall higher ionization ste for most elements at high ionization parameter, owing to the reduction in the net recombination rate. At the same time, the temperature is slightly lower, as described in the previous subsection. The opposite is true at the low ionization parameter extreme of figure 13 - the temperature is slightly greater than in figure 9 due to the enhanced recombination rates of H and He I at high densities.