THE TEMPERATURE OF EXTENDED GAS IN ACTIVE GALAXIES - EVIDENCE FOR MATTER-BOUNDED CLOUDS

We report measurements of the electron temperature at about a dozen lo cations in the extended emission-line regions of five active (Seyfert and radio) galaxies. Temperatures (T-[O III] and T[N (II])) have been determined from both the I([O III] lambda 4363)/1([O III] lambda 5007) and I([N II] lambda 5755)/I([N II] lambda 6583) ratios. T-[O III] lie s in the range (1.0-1.7) x 10(4) K. We find a strong trend for T-[O II I] to be higher than T-[N II], with the difference typically being app roximate to 5000 K. Because the critical density for collisional de-ex citation of the D-1(2) level in N II is lower than that of the same le vel in O III, the deviations of the measured intensity ratios from tho se expected for T-[O III] = T-[N II] in the low-density limit are unli kely to result from collisional de-excitation. The measured values of T-[O III] and the differences between T-[O III] and T-[N II] are very similar to those found in Galactic planetary nebulae. It is argued tha t the dominant form of energy input to the clouds is photoionization, but detailed modeling indicates that the temperature difference is too large to be accounted for in terms of photoionization of ionization-b ounded clouds. We propose instead that both matter- and ionization-bou nded clouds are present in the extended emission-line regions, with mo st of the [O III] emission originating from a hot zone in the matter-b ounded clouds and essentially al the [N II] from the ionization-bounde d clouds.