PDR Analysis with Far-infrared Diagnostic Lines in M17-SW

Photo-dissociation regions (PDRs) are the places where molecular clouds are destroyed by UV radiation of forming massive stars (eg. Hollenbach & Tielens 1999). The molecular gas is photo-dissociated and then ionized by UV radiation. Photo-electric heating heats the gas in the PDRs. Cooling happens through the dust continuum and a handful of far infrared (FIR) fine-structure lines. FIFI-LS (Colditz et al. 2012), the FIR spectrometer onboard the US-German airborne observatory, SOFIA, can map these main cooling lines efficiently.To study the heating, cooling, physical conditions and destruction rates, we observed the well-studied edge-on PDR, M17-SW with high spatial resolution in all major FIR cooling lines of the ionized and neutral medium. In this presentation, we discuss the fine-structure line and continuum maps observed by SOFIA/FIFI-LS showing the layering in this edge-on PDR. The data allows us to infer physical conditions and the energetics of the interface regions. The continuum maps together with literature data allow us to construct complete spectral energy distributions of the PDR material and the sources embedded in the PDR.The dataset presented here and its initial analysis is a comprehensive FIR view of the PDR M17-SW from the dense cloud into the ionized region at thempeak of the SED. It is a dataset to study the feedback of young massive stars on their parental cloud as it shows the ionization and dissociation front eroding the molecular cloud.References:- Colditz, Fumi et al., 2012, Proc. SPIE 8446, 844617- Hollenbach & Tielens, 1999, Rev. of Mod. Phy., 71, 173