High-mass Star Formation through Filamentary Collapse and Clump-fed Accretion in G22

How mass is accumulated from cloud-scale down to individual stars is a key open question in understanding high-mass star formation. Here, we present the mass accumulation process in a hub-filament cloud G22 which is composed of four supercritical filaments. Velocity gradients detected along three filaments indicate that they are collapsing with a total mass infall rate of about 440 $M_{\odot }$ Myr${}^{-1}$, suggesting the hub mass would be doubled in six free-fall times, adding up to $\sim 2$ Myr. A fraction of the masses in the central clumps C1 and C2 can be accounted for through large-scale filamentary collapse. Ubiquitous blue profiles in HCO${}^{+}$ $(3-2)$ and ${}^{13}$CO $(3-2)$ spectra suggest a clump-scale collapse scenario in the most massive and densest clump C1. The estimated infall velocity and mass infall rate are 0.31 km s${}^{-1}$ and $7.2\times {10}^{-4}$ $M_{\odot }$ yr${}^{-1}$, respectively. In clump C1, a hot molecular core (SMA1) is revealed by the SMA observations and an outflow-driving high-mass protostar is located at the center of SMA1. The mass of the protostar is estimated to be $11-15$ $M_{\odot }$ and it is still growing with an accretion rate of $7\times {10}^{-5}$ $M_{\odot }$ yr${}^{-1}$. The coexistent infall in filaments, clump C1, and the central hot core in G22 suggests that pre-assembled mass reservoirs (i.e., high-mass starless cores) may not be required to form high-mass stars. In the course of high-mass star formation, the central protostar, the core, and the clump can simultaneously grow in mass via core-fed/disk accretion, clump-fed accretion, and filamentary/cloud collapse.