Figure 12 shows the results of a thermal balance calculation of an optically
thin photoionized gas as a function of density and ionization
parameter. The curves correspond to ionization parameters log()=4,3,2,1
for the same power law ionizing spectrum used previously.
This demonstrates that the net effect of higher densities is
an increase in temperature at the highest densitied and lowest temperatures,
and a decrease in temperature at lower density and higher temperature,
for the reasons listed in the
previous section. We emphasize that the quantitative value of the
temperature, particularly for high ionization parameters and/or
temperatures greater than 10
K or so, depends on the detailed
shape of the ionizing spectrum over all energies, owing to the
possible importance of Compton heating and cooling (the spectral
dependence of the effects of stimulated recombination, again, have been
excluded from these results).