Continuity of accretion from clumps to Class 0 high-mass protostars in SDC335

Abstract

Context. The infrared dark cloud (IRDC) SDC335.579-0.292 (hereafter, SDC335) is a massive (~5000 M⊙) star-forming cloud which has been found to be globally collapsing towards one of the most massive star forming cores in the Galaxy, which is located at its centre. SDC335 is known to host three high-mass protostellar objects at early stages of their evolution and archival ALMA Cycle 0 data (at ~5′′ resolution) indicate the presence of at least one molecular outflow in the region detected in HNC. Observations of molecular outflows from massive protostellar objects allow us to estimate the accretion rates of the protostars as well as to assess the disruptive impact that stars have on their natal clouds during their formation. Aims. The aim of this work is to identify and analyse the properties of the protostellar-driven molecular outflows within SDC335 and use these outflows to help refine the properties of the young massive protostars in this cloud. Methods. We imaged the molecular outflows in SDC335 using new data from the Australia Telescope Compact Array of SiO and Class I CH3OH maser emission (at a resolution of ~3′′) alongside observations of four CO transitions made with the Atacama Pathfinder EXperiment and archival Atacama Large Millimeter/submillimeter Array (ALMA) CO, 13CO (~1′′), and HNC data. We introduced a generalised argument to constrain outflow inclination angles based on observed outflow properties. We then used the properties of each outflow to infer the accretion rates on the protostellar sources driving them. These accretion properties allowed us to deduce the evolutionary characteristics of the sources. Shock-tracing SiO emission and CH3OH Class I maser emission allowed us to locate regions of interaction between the outflows and material infalling to the central region via the filamentary arms of SDC335. Results. We identify three molecular outflows in SDC335 – one associated with each of the known compact H II regions in the IRDC. These outflows have velocity ranges of ~10 km s−1 and temperatures of ~60 K. The two most massive sources (separated by ~9000 AU) have outflows with axes which are, in projection, perpendicular. A well-collimated jet-like structure with a velocity gradient of ~155 km s−1 pc−1 is detected in the lobes of one of the outflows. The outflow properties show that the SDC335 protostars are in the early stages (Class 0) of their evolution, with the potential to form stars in excess of 50 M⊙. The measured total accretion rate, inferred from the outflows, onto the protostars is 1.4(±0.1) × 10−3 M⊙ yr−1, which is comparable to the total mass infall rate toward the cloud centre on parsec scales of 2.5(±1.0) × 10−3 M⊙ yr−1, suggesting a near-continuous flow of material from cloud to core scales. Finally, we identify multiple regions where the outflows interact with the infalling material in the cloud’s six filamentary arms, creating shocked regions and pumping Class I methanol maser emission. These regions provide useful case studies for future investigations of the disruptive effect of young massive stars on their natal clouds.