Properties of the photodissociated gas in NGC 6334

To investigate the properties of photodissociated gas in strong radiation f ields, the massive star formation region NGC 6334 has been mapped with the Far-Infrared Imaging Fabry-Perot Interferometer (FIFI) instrument in the fa r-infrared fine-structure transitions [C II] 158 mum, [O I] 146 mum, and [O I] 63 mum. Bright CC nl 158 mum emission is found throughout the cloud, wh ereas the CO I] 146 mum emission is associated only with the star-forming r idge. Comparison of the relative intensities of the lines with single-compo nent photodissociation region models suggests densities of n(H) similar to 10(4) cm(-3). The models imply unphysically large radiation fields for thre e sources, particularly for NGC 6334A, which is probably caused by self-abs orption in the [O I] 63 mum line. An alternative method for estimating phys ical conditions, based on the correlation between [C II] 158 mum and CO lin e intensities, is explored. This method implies hydrogen column densities o f N-H greater than or similar to 10(22-23) cm(-2), which agree well with th ose from molecular excitation models. The relative distribution of the [C I I] 158 mum and [O I] 146 mum emission supports clumpy photodissociation reg ion models that suggest the [C II] 158 mum emission arises from interclump gas and thus should be more extended than the [O I] 146 mum emission that a rises from the denser clumps. The spatial coincidence of [C II] 158 mum emi ssion peaks with minima in the molecular gas emission indicates that at lea st some of the molecular holes contain photodissociated gas. The relative p ressures of the ionized, photodissociated, and molecular gas are compared: the photodissociated and molecular gas are in approximate pressure equilibr ium, but the ionized gas is overpressurized by at least an order of magnitu de at the continuum sources.