Characterizing the nascent stages of star cluster formation is crucial for understanding their evolution. The analysis of our systematic ALMA survey of nearby, high-mass quiescent clumps revealed a puzzle: many objects with at least hundreds of solar masses of molecular material detected in single dish dust continuum data disappeared at high resolution, indicating an extended, relatively uniform distribution of material.
To investigate the nature of these sources, we analyzed ALMA archival data for three sources in the survey, representative of an early phase of high-mass star formation. Using CH3OH and N2H+ as density and kinematic tracers, we investigated the morphology and velocity structure of these regions. Remarkably, the molecular emission, even of methanol, is very extended, filling the most of the primary beam, and reveals a relatively uniform density distribution, significantly below the typical densities of established high-mass star-forming cores.
Few compact, dense cores are detected within these clumps. However, large-scale velocity gradients are observed, suggesting ongoing accretion onto the extended filamentary structures.
These findings indicate that the most extreme sources in our survey represent a very early, potentially pre-core phase of cluster formation, where mass is still being assembled from the environment before significant fragmentation occurs. Unveiling these initial conditions offers a glimpse into the very beginnings of stellar nurseries, potentially mirroring the environment where our own Sun and planet were born.
