Excitation Conditions and Energetics of the Dense Gas in M17 SW

Stars are formed in dense molecular clouds which experience radiative feedback from UV photons, X- ray from stars, embedded pre-stellar cores, YSOs, and ultra compact H II regions. The chemical and energetic conditions created by this radiative feedback can be probed with observations of multiple molecular transitions. I will show extensive maps and line spectral energy distributions (LSEDs) of the CO, HCN and HCO+ molecules (and their isotopologues) obtained toward M17 SW with the dual band receiver GREAT on board the SOFIA airborne telescope, and with the ground based APEX and IRAM 30m telescopes. The excitation conditions of the three species are estimated simultaneously using the same density and temperature in a two-phase non-LTE radiative transfer model of the LSEDs at four selected positions. The LSED shape, particularly the high-J tail of the CO lines observed with SOFIA/GREAT, is distinctive for the underlying excitation conditions. The energy balance at selected positions is also studied, including the measured magnetic fields. These results have just been accepted for publication in A&A.