High-resolution APEX/LAsMA ¹²CO and ¹³CO (3–2) observation of the G333 giant molecular cloud complex

II. Survival and gravitational collapse of dense gas structures under feedback

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: jwzhou@mpifr-bonn.mpg.de
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China

Received: 6 July 2023
Accepted: 7 September 2023

Abstract

Context. Feedback from young massive stars has an important impact on the star formation potential of their parental molecular clouds.

Aims. We investigate the physical properties of gas structures under feedback in the G333 complex using data of the ¹³CO J = 3–2 line observed with the LAsMA heterodyne camera on the APEX telescope.

Methods. We used the Dendrogram algorithm to identify molecular gas structures based on the integrated intensity map of the ¹³CO (3–2) emission, and extracted the average spectra of all structures to investigate their velocity components and gas kinematics.

Results. We derive the column density ratios between different transitions of the ¹³CO emission pixel by pixel, and find the peak values N₂₋₁/N₁₋₀ ≈ 0.5, N₃₋₂/N₁₋₀ ≈ 0.3, and N₃₋₂/N₂₋₁ ≈ 0.5. These ratios can also be roughly predicted by the nonlocal thermodynamic equilibrium (NLTE) molecular radiative transfer code RADEX for an average H₂ volume density of ~4.2 × 10³ cm⁻³. A classical virial analysis does not reflect the true physical state of the identified structures, and we find that external pressure from the ambient cloud plays an important role in confining the observed gas structures. For high-column-density structures, velocity dispersion and density show a clear correlation that is not seen for low-column-density structures, indicating the contribution of gravitational collapse to the velocity dispersion. Branch structures show a more significant correlation between 8 μm surface brightness and velocity dispersion than leaf structures, implying that feedback has a greater impact on large-scale structures. For both leaf and branch structures, σ − N * R always has a stronger correlation compared to σ − N and σ − R. The scaling relations are stronger, and have steeper slopes when considering only self-gravitating structures, which are the structures most closely associated with the Heyer relation.

Conclusions. Although the feedback disrupting the molecular clouds will break up the original cloud complex, the substructures of the original complex can be reorganized into new gravitationally governed configurations around new gravitational centers. This process is accompanied by structural destruction and generation, and changes in gravitational centers, but gravitational collapse is always ongoing.