ATOMS: ALMA Three-millimeter Observations of Massive Star-forming regions – XV. Steady Accretion from Global Collapse to Core Feeding in Massive Hub-filament System SDC335

We present ALMA Band-3/7 observations towards “the Heart” of a massive hub-filament system (HFS) SDC335, to investigate its fragmentation and accretion. At a resolution of 0.03 pc, 3mm continuum emission resolves two massive dense cores MM1 and MM2, with 383¹¸234, and 120 𝑀sun  (10–24% mass of “the Heart”) and 74¸ 47, and 24 solar masses, respectively. With a resolution down to 0.01 pc, 0.87mm continuum emission shows MM1 further fragments into six condensations and multi-transition lines of H2CS provide temperature estimation. The relation between separation and mass of condensations at a scale of 0.01 pc favors turbulent Jeans fragmentation where the turbulence seems to be scale-free rather than scale-dependent. We use the H13CO¸ 𝐽 = 1 - 0 emission line to resolve the complex gas motion inside “the Heart” in position-position-velocity space.We identify four major gas streams connected to large-scale filaments, inheriting the anti-clockwise spiral pattern. Along these streams, gas feed the central massive core MM1. Assuming an inclination angle of 45¹ 15º  and a H13CO¸ abundance of 5¹ 3º   10􀀀11, the total mass infall rate is estimated to be 2.40¹ 0.78º   10􀀀3 𝑀  yr􀀀1, numerically consistent with the accretion rates derived from the clump-scale spherical infall model and the core-scale outflows. The consistency suggests a continuous, near steady-state, and efficient accretion from global collapse, therefore ensuring core feeding. Our comprehensive study of SDC335 showcases the detailed gas kinematics in a prototypical massive infalling clump, and calls for further systematic and statistical studies in a large sample.