G11.92-0.61 MM1: A Keplerian disc around a massive young proto-O star
  The formation process of massive stars is not well understood, and
advancement in our understanding benefits from high resolution observations and
modelling of the gas and dust surrounding individual high-mass (proto)stars.
Here we report sub-arcsecond (<1550 au) resolution observations of the young
massive star G11.92-0.61 MM1 with the SMA and VLA. Our 1.3 mm SMA observations
reveal consistent velocity gradients in compact molecular line emission from
species such as CH$_3$CN, CH$_3$OH, OCS, HNCO, H$_2$CO, DCN and CH$_3$CH$_2$CN,
oriented perpendicular to the previously reported bipolar molecular outflow
from MM1. Modelling of the compact gas kinematics suggests a structure
undergoing rotation around the peak of the dust continuum emission. The
rotational profile can be well fit by a model of a Keplerian disc, including
infall, surrounding an enclosed mass of 30-60M$_{\odot}$, of which
2-3M$_{\odot}$ is attributed to the disc. From modelling the CH$_3$CN emission,
we determine that two temperature components, of 150 K and 230 K, are required
to adequately reproduce the spectra. Our 0.9 and 3.0cm VLA continuum data
exhibit an excess above the level expected from dust emission; the full
centimetre-submillimetre wavelength spectral energy distribution of MM1 is well
reproduced by a model including dust emission, an unresolved hypercompact
H{\i}{\i} region, and a compact ionised jet. In combination, our results
suggest that MM1 is an example of a massive proto-O star forming via disc
accretion, in a similar way to that of lower mass stars.
