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 cm
. 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.