EPoS Contribution
EPoS Contribution
From core to disk fragmentation in high-mass star formation

Aida Ahmadi
Leiden Obs., Leiden, NL
There is growing consensus that the formation of high-mass stars proceeds through disk accretion, similar to that of lower mass stars. To this end, we have undertaken a large observational program (CORE) making use of interferometric observations from the NOrthern Extended Millimetre Array (NOEMA) for a sample of 20 high-mass protostellar objects in the 1.3 millimetre wavelength regime reaching ~0.4" resolution (800 au at 2 kpc). We find rotational signatures in dense gas perpendicular to bipolar molecular outflows in most regions (see attached figure). Modelling the level populations of various rotational transitions of the dense gas tracer CH3CN, we find the disk candidates to be on average warm (~200 K). Studying the Toomre stability of the disk-like structures reveals that most high-mass young stellar objects are gravitationally unstable and prone to disk fragmentation. Since most high-mass stars are found to have companions, disk fragmentation seems to be an important mechanism by which such systems may be formed. While observations at hundreds of au resolution have now shown that rotational signatures are common around such young and massive accreting protostars, it is difficult to differentiate between rotating and infalling envelope material and true disk structures which likely reside on much smaller scales. In this talk, I will take you on a tour across scales from our findings at hundreds of au resolution with NOEMA reaching down to sub 100 au observations with ALMA. In particular, I will showcase observations of a unique high-mass protobinary system observed with two ALMA configurations covering largest angular scales of 5000 au down to 90 au (0.03"). The protobinary components have a separation of ~200 au and are engulfed in a spatially-resolved circumbinary disk. The system resides within a dense cluster of gas and dust with a complex structure extending ~0.1 pc in size and containing many fragmented cores. I will put into context the dynamics of such regions and how different modes of fragmentation can contribute to the final stellar mass distribution in high-mass star forming regions.
Caption: Intensity-weighted peak velocity (first moment) maps of CH3CN (12-11) K=3, showing the dense gas kinematics for 15 of the 20 sources in the CORE survey. The contours correspond to the 1.37 mm continuum. The blue and red arrows correspond to the estimated directions of bipolar blueshifted and redshifted molecular outflows, respectively. The dotted lines indicate the position of the strongest velocity gradient tracing the disk. The synthesised beam is shown in the bottom left corner and a scale bar in the bottom right corner of each panel.
Collaborators:
H. Beuther, MPIA, DE
R. Kuiper, U Tuebingen, DE
CORE Team
Key publication

Suggested Session: High Mass