Investigating fragmentation of gas structures in OB cluster-forming
  molecular clump G33.92+0.11 with 1000 AU resolution observations of ALMA
  We report new, $\sim$1000 AU spatial resolution observations of 225 GHz dust
continuum emission towards the OB cluster-forming molecular clump G33.92+0.11.
On parsec scales, this molecular clump presents a morphology with several
arm-like dense gas structures surrounding the two central massive ($\gtrsim$100
$M_{\odot}$) cores. From the new, higher resolution observations, we identified
28 localized, spatially compact dust continuum emission sources, which may be
candidates of young stellar objects. Only one of them is not embedded within
known arm-like (or elongated) dense gas structures. The spatial separations of
these compact sources can be very well explained by Jeans lengths. We found
that G33.92+0.11 may be consistently described by a marginally centrifugally
supported, Toomre unstable accretion flow which is approximately in a face-on
projection. The arm-like overdensities are natural consequence of the Toomre
instability, which can fragment to form young stellar objects in shorter time
scales than the timescale of the global clump contraction. On our resolved
spatial scales, there is not yet evidence that the fragmentation is halted by
turbulence, magnetic field, or stellar feedback.
