2022ApJ...926....4M

This paper investigates the impact of radiative and mechanical feedback from O-type stars on their parent molecular clouds and the triggering of formation of a future generation of stars. We study the infrared bubble S111 created by the embedded massive stellar cluster G316.80-0.05. A significant fraction of gas in shells created due to the compression of the ambient medium by expanding bubbles is photodissociated by the stellar radiation. The kinematics of the shells are thus best studied using spectroscopic observations of singly ionized carbon, the most dominant species. We have used velocity-resolved maps of the ²P_3/2 - ²P_1/2 transition of [C II] at 158 µm, the J = 2-1 transition of ¹³CO and C¹⁸O, and the J = 1-0 transition of HCO⁺ to study the rim of the bubble S111 that partly coincides with the southern part of the infrared dark ridge G316.75. The [C II] spectra conclusively show evidence of a shell expanding with a moderate velocity of ∼7 km s^–1, which amounts to a kinetic energy that is ∼0.5-40 times the thermal energy of the H II region. The pressure causing the expansion of the H II region arises mainly from hydrogen ionization and dust-processed radiation. Among the far-infrared sources located in compressed shells, we find the core G316.7799-0.0942 to show broad spectral features consistent with outflow activity and conclude that it is a site of active star formation. Based on the age of the H II region we conclude that this expanding H II region is responsible for triggering the current star formation activity in the region.