ATOMS-QUARKS survey: Inflow and infall in massive protocluster G318.049+00.086: Evidence of competitive accretion

We present a gas kinematic study of the massive protocluster G318.049+00.086. The protocluster is reported to contain 12 prestellar core candidates and 4 protostellar cores. Filamentary structures are identified using the 1.3 mm dust continuum map, with four of them converge into a dense central region, forming a hub-filament system (HFS). High velocity gradients (10 - 20 km s$^{-1}$ pc$^{-1}$) derived from PV analysis of H$^{13}$CO$^{+}$ emission along three of those filaments are suggestive of mass inflow onto the central hub. A mass inflow rate higher than $10^{3}$ M$_{\odot}$ Myr$^{-1}$ along the filaments is indicating that the central hub is capable of forming massive star(s). Investigation of H$^{13}$CO$^{+}$ and CCH spectral profiles revealed the majority of the cores having the characteristic blue asymmetric line profiles, typical signature of gravitational collapse. The remaining few cores showed red asymmetric profiles, indicative of gas expansion. Also, the derived mass infall rates for the protostellar cores in hub-region is significantly higher in comparison to those located along the filaments. The mass-radius relationship of the cores revealed that the cores with red profiles reside in the massive star formation regime. However, the global velocity gradient along the filaments suggests that these particular cores are losing material to the hub. Our results are supporting a competitive accretion scenario of massive star formation where gas is expected to be funnelled from less gravitationally dominant cores to the cores located at the gravitationally favorable position.

💡 Research Summary

**
The authors present a multi‑scale kinematic study of the massive protocluster G318.049+00.086 using ALMA data from three complementary surveys: ATOMS (3 mm continuum and line data), QUARKS (high‑resolution 1.3 mm continuum), and ASSEMBLE (high‑density tracers). The region lies at a distance of ~2.9 kpc, has a total gas mass of ~1 × 10³ M⊙, and a dust temperature of ~27 K. Previous work identified 12 prestellar core candidates and 4 protostellar cores within the cluster.

The authors first map the filamentary network. By applying the FilFinder algorithm to the H¹³CO⁺(1–0) moment‑0 map and to the 1.3 mm continuum, they recover four main filaments (named F1–F4) that converge onto a dense central hub, forming a classic hub‑filament system (HFS). Twelve of the fourteen identified cores are associated with these filaments, confirming that the bulk of the dense gas is organized in a filamentary geometry.

Velocity‑gradient analysis along the filament spines, performed with position‑velocity (PV) diagrams of H¹³CO⁺, reveals systematic gradients of 10–20 km s⁻¹ pc⁻¹. Assuming the gradients trace longitudinal inflow rather than rotation, the authors calculate mass inflow rates of >10³ M⊙ Myr⁻¹ per filament, yielding a total inflow of several × 10³ M⊙ Myr⁻¹ into the hub. Such a high inflow is sufficient to sustain the formation of massive stars in the hub region.

To probe small‑scale collapse, the authors examine the line profiles of H¹³CO⁺(1–0) and CCH (J = 3/2–1/2). The majority of cores display blue‑asymmetric profiles, a classic signature of infall, while a minority exhibit red‑asymmetric profiles, indicative of expansion or outflow. The protostellar cores located in the hub have significantly higher inferred infall rates than the cores situated along the filaments, consistent with a scenario where material is funneled from the larger‑scale network into the most gravitationally favorable locations.

A mass‑radius (M–R) analysis shows that cores with red‑asymmetric profiles fall within the high‑mass star formation regime (M > 8 M⊙, R < 0.1 pc). However, the global filamentary velocity gradient suggests that these cores are losing mass to the hub rather than accreting it, reinforcing the idea of competitive accretion: less massive or less centrally located cores feed the growth of the central massive objects.

The authors discuss their findings in the context of competing massive‑star formation theories. The turbulent‑core model predicts isolated massive prestellar cores that collapse independently; the observations here, with widespread filamentary inflow and a clear mass‑transfer hierarchy, do not support this picture. Instead, the data favor clump‑fed models, particularly competitive accretion, where the gravitational potential of the whole protocluster drives gas toward the deepest potential well (the hub). The observed large‑scale converging flows also echo predictions of the Global Hierarchical Collapse (GHC) model, which envisions multiscale, anisotropic collapse with material streaming along filaments onto dense hubs.

In summary, G318.049+00.086 provides a compelling observational case of a hub‑filament system with high‑velocity, high‑mass inflow, simultaneous signatures of core‑scale infall and expansion, and a mass distribution that aligns with competitive accretion. The study demonstrates how gas is redistributed from peripheral, less gravitationally bound cores to the central hub, supplying the material needed for massive star formation and offering strong empirical support for clump‑fed, competitive‑accretion scenarios.