SOFIA FEEDBACK survey: Exploring the kinetics of the stellar wind driven shell of RCW 49

One of the most important problems in modern astrophysics is to understand the role of massive stars in driving various physical and chemical processes in the Interstellar Medium (ISM). Massive stars inject an immense amount of mechanical and radiative energy into their immediate vicinity. Stellar winds are responsible for the mechanical energy input, which can push the gas into shell-like structures (as in the Rosette Nebula, Waering et al. 2018 and in the Orion Nebula, Pabst et al. 2019). The radiative energy input comes from the heating of gas through stellar extreme-ultraviolet (EUV, hν > 13.6 eV) and far-UV (FUV, 6 < hν < 13.6 eV) photons that can ionize atoms, dissociate molecules and heat the gas giving rise to H II regions and photodissociation regions (PDRs). These stellar feedback mechanisms power the expansion of H II regions and shock fronts causing morphological features that appear as shells or bubbles in the ISM. We unveil the stellar wind driven shell of the luminous massive star-forming region of RCW 49 using SOFIA FEEDBACK observations of the [C II] 158 μm line. The complementary dataset of the ¹²CO and ¹³CO J = 3 - 2 transitions is observed by the APEX telescope and probes the dense gas toward RCW 49. Using the high spatial and spectral resolution provided by the SOFIA and APEX telescopes, we disentangle the shell from a complex set of individual components of gas centered around RCW 49. We find that the shell of radius ~ 6 pc is expanding at a velocity of 13 km s^-1 toward the observer. Comparing our observed data with the ancillary data in X-Ray, infrared, sub-millimeter and radio wavelengths, we investigate the morphology of the region. The shell has a well defined eastern arc, while the western side is blown open and is venting plasma further into the west. Though the stellar cluster, which is ~ 2 Myr old gave rise to the shell, it only gained momentum relatively recently as we calculate the shell’s expansion lifetime ~ 0.27 Myr, making the Wolf-Rayet star WR20a a likely candidate responsible for the shell’s re-acceleration.