[O I] 63 micron absorption in NGC 6334

The [O I] 63 mu m transition has been imaged around five far-infrared (FIR) and radio continuum sources in the southern massive star formation region NGC 6334. The [O I] 63 mu m line is found in absorption toward the FIR cont inuum source NGC 6334V. This is only the second case in which the [O I] 63 mu m line has been seen in absorption against a continuum source. From the depth of the absorption line, the minimum column density of oxygen is calcu lated to be N(O-0) greater than or similar to 5 x 10(18) cm(-2). This amoun t of oxygen is consistent with [O I] 63 mu m absorption due to atomic gas i n the foreground molecular cloud. The [O I] 63 mu m line is found in emission toward the other four sources o bserved: NGC 6334, sources A, C, D, and E. Single-component photodissociati on region (PDR) models suggest densities of n similar to 10(4) cm(-3) for t hese sources, based on previously observed [O I] 145 mu m and [C II] 158 mu m intensities. However, unphysically large far-ultraviolet (FUV) fields ar e implied for three of the sources, particularly for NGC 6334A. Neither one - nor two-component photodissociation region models can explain the anomalo usly low [O I] 63 mu m intensity toward NGC 6334A nor the absorption toward NGC 6334V. We suggest that self-absorption of the [O I] 63 mu m line, such as has been suggested toward DR 21, is suppressing the observed [O I] 63 m u m intensity. This underestimate leads to an overestimate of the derived F UV field strengths throughout NGC 6334. The discovery of several more star- forming sites in which the [O I] 63 mu m is in absorption or is self-absorb ed implies that this line is not always a reliable PDR diagnostic because t he PDR models do not treat the radiative transfer through the molecular clo ud.