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Molecular clouds (MCs) are active sites of star formation in galaxies, and their formation and evolution are largely affected by stellar feedback. This includes outflows and winds from newly formed stars, radiation from young clusters, and supernova explosions. High-resolution molecular line observations allow for the identification of individual star-forming regions and the study of their integrated properties. Moreover, state-of-the-art simulations are now capable of accurately replicating the evolution of MCs, including all key stellar feedback processes. We present¹³CO(2–1) synthetic observations of the STARFORGE simulations produced using the radiative transfer code RADMC-3D, matching the observational setup of the SEDIGISM survey. From these synthetic observations, we identified the population of MCs using hierarchical clustering and analysed them to provide insights into the interpretation of observed MCs as they evolve. The flux distributions of the post-processed synthetic observations and the properties of the MCs, namely, radius, mass, velocity dispersion, virial parameter, and surface density, are consistent with those of SEDIGISM. Both samples of MCs occupy the same regions in the scaling relation plots; however, the average distributions of MCs at different evolutionary stages do not overlap on the plots. This highlights the reliability of our approach in modelling SEDIGISM and suggests that MCs at different evolutionary stages contribute to the scatter in observed scaling relations. We study the trends in MC properties, morphologies, and fragmentation over time to analyse their physical structure as they form, evolve, and are destroyed. MCs appear as small diffuse cloudlets in early stages, and this is followed by their evolution to filamentary structures before being shaped by stellar feedback into 3D bubbles and getting dispersed. These trends in the observable properties of MCs are consistent with other realisations of simulations and provide strong evidence that clouds exhibit distinct morphologies over the course of their evolution. 

Stars form in dense cores within molecular clouds, and newly formed stars influence their natal environments. How stellar feedback impacts core properties and evolution has been the subject of extensive investigation. We performed a hierarchical clustering (dendrogram) analysis of a STARFORGE (STAR FORmation in Gaseous Environments) simulation, modelling a giant molecular cloud to identify gas overdensities (cores) and study changes in their radius, mass, velocity dispersion, and virial parameter with respect to stellar feedback. We binned these cores on the basis of the fraction of gas affected by protostellar outflows, stellar winds, and supernovae and analysed the property distributions for each feedback bin. We find that cores that experience more feedback influence are smaller. Feedback notably enhances the velocity dispersion and virial parameter of the cores, more so than it reduces their radius. This is also evident in the linewidth–size relation, according to which cores in higher-feedback bins exhibit higher velocities than their similarly sized pristine counterparts. We conclude that stellar feedback mechanisms, which impart momentum to the molecular cloud, simultaneously compress and disperse the dense molecular gas. 

Context.Molecular outflows are believed to be a key ingredient in the process of star formation. The molecular outflow associated with DR21 Main in Cygnus-X is one of the most extreme molecular outflows in the Milky Way in terms of mass and size. The outflow is suggested to belong to a rare class of explosive outflows formed by the disintegration of protostellar systems. Aims.We aim to explore the morphology, kinematics, and energetics of the DR21 Main outflow, and to compare those properties to confirmed explosive outflows in order to unravel the underlying driving mechanism behind DR21. Methods.We studied line and continuum emission at a wavelength of 3.6 mm with IRAM 30 m and NOEMA telescopes as part of the Cygnus Allscale Survey of Chemistry and Dynamical Environments (CASCADE) program. The spectra include (J= 1−0) transitions of HCO⁺, HCN, HNC, N₂H⁺, H₂CO, and CCH, which trace different temperature and density regimes of the outflowing gas at high velocity resolution (~0.8 km s⁻¹). The map encompasses the entire DR21 Main outflow and covers all spatial scales down to a resolution of 3″ (~0.02 pc). Results.Integrated intensity maps of the HCO⁺emission reveal a strongly collimated bipolar outflow with significant overlap of the blueshifted and redshifted emission. The opening angles of both outflow lobes decrease with velocity, from ~80 to 20° for the velocity range from 5 to 45 km s⁻¹relative to the source velocity. No evidence is found for the presence of elongated, “filament-like” structures expected in explosive outflows. N₂H⁺emission near the western outflow lobe reveals the presence of a dense molecular structure, which appears to be interacting with the DR21 Main outflow. Conclusions.The overall morphology as well as the detailed kinematics of the DR21 Main outflow are more consistent with a typical bipolar outflow than with an explosive counterpart.