Stellar Feedback on the Earliest Stage of Massive Star Formation.

We report SOFIA/GREAT observations of high-J CO lines and [C ii ] observations of the super star cluster candidate H72.97-69.39 in the Large Magellanic Cloud (LMC), which is in its very early formation stage. We use our observations to determine if shocks are heating the gas or if photon-dominated regions (PDRs) are being heated by local far-UV radiation. We use a PDR model and a shock model to determine whether the CO and [C ii ] lines arise from PDRs or shocks. We can reproduce the observed high-J CO and [C ii ] emission with a clumpy PDR model with the following properties: a density of 10^4.7 cm⁻³, a mass of 10⁴M_⊙, and UV radiation of 10^3.5 in units of Draine field. Comparison with the ALMA beam-filling factor suggests a higher density within the uncertainty of the fit. We find the lower-limit [C ii ]/total infrared (TIR) ratio (ϵ) traced by [C ii ]/TIR to be 0.026%, lower than other known young star-forming regions in the LMC. Our shock models may explain the CO (16−15) and CO (11−10) emission lines with shock velocity of 8–11 km s⁻¹, pre-shock density of 10⁴–10⁵ cm⁻³, and G_UV = 0 in units of Draine field. However, the [C ii ] line emission cannot be explained by a shock model, thus it is originating in a different gas component. Observations of [O i ] 63 μm predicted to be 1.1 × 10⁻¹³ W m⁻² by PDR models and 7.8 × 10⁻¹⁵ W m⁻² by shock models will help distinguish between the PDR and shock scenarios. [ABSTRACT FROM AUTHOR]