Global collapse of molecular clouds as a formation mechanism for the most massive starsReport as inadecuate

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* Corresponding author 1 Cardiff School of Physics and Astronomy 2 AIM - UMR 7158 - UMR E 9005 - Astrophysique Interactions Multi-échelles 3 Jodrell Bank Centre for Astrophysics 4 LAB - Laboratoire d-Astrophysique de Bordeaux Pessac 5 ESO - European Southern Observatory 6 OAR - INAF - Osservatorio Astronomico di Roma

Abstract : The relative importance of primordial molecular cloud fragmentation versus large-scale accretion still remains to be assessed in the context of massive core-star formation. Studying the kinematics of the dense gas surrounding massive-star progenitors can tell us the extent to which large-scale flow of material impacts the growth in mass of star-forming cores. Here we present a comprehensive dataset of the 5500±800 M⊙ infrared dark cloud SDC335.579-0.272 hereafter SDC335, which exhibits a network of cold, dense, parsec-long filaments. Atacama Large Millimeter Array ALMA Cycle 0 observations reveal two massive star-forming cores, MM1 and MM2, sitting at the centre of SDC335 where the filaments intersect. With a gas mass of 545-385+770 M⊙ contained within a source diameter of 0.05 pc, MM1 is one of the most massive, compact protostellar cores ever observed in the Galaxy. As a whole, SDC335 could potentially form an OB cluster similar to the Trapezium cluster in Orion. ALMA and Mopra single-dish observations of the SDC335 dense gas furthermore reveal that the kinematics of this hub-filament system are consistent with a global collapse of the cloud. These molecular-line data point towards an infall velocity Vinf = 0.7 ± 0.2 km s-1, and a total mass infall rate Ṁinf ≃ 2.5±1.0 × 10-3 M⊙ yr-1 towards the central pc-size region of SDC335. This infall rate brings 750±300 M⊙ of gas to the centre of the cloud per free-fall time tff = 3 × 105 yr. This is enough to double the mass already present in the central pc-size region in 3.5-1.0+2.2 × tff. These values suggest that the global collapse of SDC335 over the past million year resulted in the formation of an early O-type star progenitor at the centre of the cloud’s gravitational potential well.

Keywords : stars: massive stars: formation ISM: kinematics and dynamics ISM: clouds ISM: structure

Author: N. Peretto - G. A. Fuller - A. Duarte-Cabral - A. Avison - P. Hennebelle - J. E. Pineda - Ph. André - S. Bontemps - F. Motte - N



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