2023A&A...679A..66S

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^–1 relative 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.