Star Formation Triggered by the expanding bubble S111

TL;DR

This study examines how the expanding bubble S111, driven by feedback from massive stars, triggers star formation in the surrounding molecular cloud through detailed spectroscopic observations.

Contribution

It provides observational evidence linking the expansion of the H II region S111 to the initiation of new star formation in its vicinity.

Findings

The shell of S111 is expanding at ~7 km/s.

The kinetic energy of the shell is comparable to the thermal energy of the H II region.

Active star formation is occurring in the compressed shell region.

Abstract

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 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 the velocity-resolved maps of the $^2{\rm P}_{3/2}\rightarrow ^2{\rm P}_{1/2}$ transition of [C II] at 158 micron, 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, 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 the hydrogen ionization and the dust-processed radiation. Among the far-infrared sources located in the 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 the triggering of the current star formation activity in the region.