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

Abstract

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, 3 mm continuum emission resolves two massive dense cores MM1 and MM2, with 383( +234 −120 ) 𝑀 (10-24% mass of "the Heart") and 74( +47 −24 ) 𝑀 , respectively. With a resolution down to 0.01 pc, 0.87 mm continuum emission shows MM1 further fragments into six condensations and multi-transition lines of H 2 CS 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 H 13 CO + 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 45(±15) • and a H 13 CO + abundance of 5(±3) × 10 −11 , the total mass infall rate is estimated to be 2.40(±0.78) × 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.