Stellar Feedback on the Earliest Stage of Massive Star Formation

Abstract

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 10⁴ M_⊙, 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 (ɛ) 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 ] 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.