Oral Presentation

The 70 μm-dark high-mass clump G 28.34 S: a prestellar or protostellar clump?

Author(s): S. Feng (MPE), H. Beuther (MPIA), Q. Zhang (CfA), H. B. Liu (ESO), Z. Zhang (ESO), K. Wang (ESO), and K. Qiu (NJU)

Presenter: Siyi Feng (Max-Planck-Institut für Extraterrestrische Physik)

Whether high-mass stars form via a quick global collapse of dense molecular gas core, or via the competitive accretion of a cluster of low-mass (proto)stars, is a fundamental question in high-mass cluster-formation. Identifying and resolving the initial conditions of high-mass star-formation is the first step towards addressing this question.
The 70μm dark molecular clump G28.34 S stands out from our EPoS IRDC sample for its uniqueness. Discovered around the southern edge of the filamentary IRDC, this dense (> 10^5 cm−3), cold (13–16 K), and dark (< 10L⊙) source was previously considered as one of the best candidates for hosting high-mass “starless" cores. 1 mm/3 mm line survey with IRAM-30 m towards this region at 0.8 pc-scale indicates its young evolutionary stage, including a high ionization ratio (> 10^(−7)), a large number of nitrogen-bearing species, a significant depletion of CO, and the linewidths suggestive that non-thermal motions dominant the support against gravity in the fragments of this clump.
Surprisingly, observing the SiO (2-1) and (6-5) lines with the NOEMA and SMA at a linear resolution of 0.1 pc, we detected a W-E oriented outflow towards the > 40 M⊙ core S-A. This bipolar outflow, is confirmed by the ALMA archival SiO (5-4) data, from which we found the high-velocity gas (up to 40 km /s relative to the quiescent cloud) revealing a more compact lobe projectionally closer to the dust center, indicating that the central source may be in an early evolutionary stage of forming a high-mass protostar.
Discussing the possible accretion scenarios of the outflow-powering young stellar object, we argue that the molecular line emission and the molecular outflows may provide a better indication of the accretion history when forming young stellar object, than that from a snapshot observations of the present bolometric luminosity.