Emission of CO, C I, and C II in W3 Main

Abstract

\n We used the KOSMA 3m telescope to map the core\n $7'$ $\\times$ $5'$ of the Galactic massive star forming region W3 Main\n in the two fine structure lines of atomic carbon and four mid-J\n transitions of CO and 13CO. The maps are centered on the\n luminous infrared source IRS 5 for which we obtained ISO/LWS\n data comprising four high-J CO transitions, [$\\ion{C}{ii}$], and [$\\ion{O}{i}$] at 63 and $145~\\mu$m. In combination with a KAO map of integrated\n line intensities of [$\\ion{C}{ii}$] [CITE], this data set\n allows us to study the physical structure of the molecular cloud\n interface regions where the occurence of carbon is believed to\n change from C+ to C0, and to CO. The molecular gas in\n W3 Main is warmed by the far ultraviolet (FUV) field created by\n more than a dozen OB stars. Detailed modelling shows that most\n of the observed line intensity ratios and absolute intensities\n are consistent with a clumpy photon dominated region (PDR) of a few hundred unresolved clumps per 0.84 pc beam, filling between 3 and 9% of the volume, with a typical clump radius of 0.025 pc\n ($2.2''$), and typical mass of 0.44 $M_{\\odot}$.\n The high-excitation lines of CO stem from a $100{-}200$ K layer, as\n do the [$\\ion{C}{i}$] lines. The bulk of the gas mass is however at lower\n temperatures. \n \n \n