Oral Presentation
Defining the initial conditions of high-mass star formation with ALMA
Presenter: Kaho Morii (The University of Tokyo/NAOJ)
Physical properties in infrared dark clouds (IRDCs) provide insights into the initial conditions of high-mass stars and stellar clusters formation. As part of the ALMA Survey of 70 um dark High-mass clumps in Early Stages (ASHES) project, we have mosaicked thirty-nine IRDCs with ALMA at 1.3 mm, resulting in an angular resolution of 1''.2 (~0.02 pc at 4 kpc). Targets are 70µm-dark, cold, massive, and dense clumps, the best sample to study the earliest stage of the high-mass star formation.
Dust continuum emission reveals the internal structure of IRDCs and the unprecedented amount of 839 cores, making this the largest sample of IRDCs observed with ALMA so far. We find less than 1% of cores have masses higher than 27 Msun, and these cores are all gravitationally bound associated with outflows. We have no high-mass (>27 Msun) core that has no detections of outflow and warm gas tracers. Although at least one high-mass core is expected in each clump from the clump mass, cores with the largest mass lack sufficient mass to form high-mass stars without additional mass feeding in 90% of our sample (35/39). We also find a weak correlation between the maximum core mass in each clump and their clump mass contrary to the strong correlation found in stellar clusters between the maximum stellar mass and cluster mass, implying that the maximum core mass is not determined by the natal clump mass at least in the very early stages traced in the ASHES. We find no preferred locations for the formation of the most massive cores (e.g., in hub-filament systems or clump centers) and only a few tentative detections of mass segregation.
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