CII, CI, and CO in the Massive Star Forming Region W3 Main

We used the KOSMA 3m telescope to map the core 7′ × 5′ of the Galactic massive star forming region W3 Main in the two fine structure lines of atomic carbon and four mid-J transitions of CO and 13CO. In combination with a map of singly ionized carbon (Howe et al. 1991), and ISO/LWS data at the center position, these data sets allow to study in detail the physical structure of the photon dominated cloud interface regions (PDRs) where the occurance of carbon changes from Cii to Ci to CO. The physical and chemical processes in these layers are governed by FUV radiation. Depending on the induced chemistry, the critical densities, and energy levels of their transitions, the lines of [Cii], [Ci], and CO serve as probes to trace the different temperature and density regimes.