High-resolution LAsMA 12CO and 13CO observation of the G305 giant molecular cloud complex I. Feedback on the molecular gas

Context: Understanding the effect of feedback, interaction of young massive stars with their parental giant molecular clouds, is of central importance for studies of the interstellar medium and star formation.

Aims: We observed the G305 star-forming complex in the J = 3–2 lines of 12CO and 13CO to investigate how molecular gas surrounding the central stellar clusters is being impacted by feedback.

Methods: The Atacama Pathfinder EXperiment (APEX) telescope’s Large APEX sub-Millimeter Array (LAsMA) multibeam receiver was used to observe the region. Excitation temperatures and column density maps were produced. Combining our data with data from the structure, excitation, and dynamics of the inner Galactic interstellar medium survey resulted in a 13CO J = 3−2∕2−1 excitation map. To verify whether feedback from stellar clusters is responsible for exciting the gas, the distribution of CO excitation was compared with that of 8 μm emission imaged with Spitzer, which is dominated by UV-excited emission from polycyclic aromatic hydrocarbons. Line centroid velocities, as well as stacked line profiles were examined to investigate the effect of feedback on the gas dynamics.

Results: Line profiles along radially outward directions demonstrate that the excitation temperature and 13CO J = 3−2∕2−1 ratio increase steeply by factors of ~2–3 at the edge of the denser gas traced by 13CO that faces the hot stars at the center of the complex and steadily decreases away from it. The column density also increases at the leading edge, but it does not always decrease steadily outward. Regions with a higher 8 μm flux have higher median excitation temperatures, column densities, and 13CO J = 3−2∕2−1 ratio. The centroid velocity probability distribution function of the region shows exponential wings, indicative of turbulence driven by strong stellar winds. Stacked spectra in regions with stronger feedback have higher skewness and narrower peaks with pronounced wings compared to regions with weaker feedback.

Conclusions: Feedback from the stellar cluster in G305 has demonstrable effects on the excitation as well as on the dynamics of the giant molecular cloud.