The PDR in M17-SW analyzed with FIFI-LS onboard SOFIA
Abstract
Photo-dissociation regions (PDRs) are the places where molecular clouds are destroyed by UV radiation of forming massive stars. The molecular gas is photo-dissociated and then ionized by UV radiation. The UV radiation below 13.6 eV heats the gas via the photo-electric effect on dust grains. Cooling happens through the dust continuum and a handful of far infrared (FIR) fine-structure lines. FIFI-LS, the FIR spectrometer onboard the US-German airborne observatory, SOFIA, can map these main cooling lines efficiently. 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. By comparing the observed line intensities to model predictions we mapped the physical conditions of the ionized and neutral layer of the PDR by The [OIII] line ratio readily provides the electron density maps in the ionized layer just above the PDR. The median electron density in that area is about 103cm-3. The analysis of the [OI], [CII], CO and continuum emission with the PDR Tool box allowed us to map the gas density and UV radiation field strength over the region. The gas density in the PDR is varies between 105 and 106cm-3. The UV field is about 104.4 in Habing units. We also estimated the optical depth effects to the [OIII]63μm line and the contribution of the PDR to the ubiquitous [CII] emission for each map position. While the applied model is comparatively simple, a consistent picture of the spatial variation of the physical parameters over the mapped region could be derived. Based on these findings the processes and energetics in the PDR can be studied further possibly by applying more detailed models together with more data from other wavelengths.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23331101K