A Face-on Accretion System in High-Mass Star-Formation: Possible Dusty
  Infall Streams within 100 AU
  We report on interferometric observations of a face-on accretion system
around the High-Mass young stellar object, G353.273+0.641. The innermost
accretion system of 100 au radius was resolved in a 45 GHz continuum image
taken with the Jansky-Very Large Array. Our spectral energy distribution
analysis indicated that the continuum could be explained by optically thick
dust emission. The total mass of the dusty system is $\sim$ 0.2 $M_{\sun}$ at
minimum and up to a few $M_{\sun}$ depending on the dust parameters. 6.7 GHz
CH$_{3}$OH masers associated with the same system were also observed with the
Australia Telescope Compact Array. The masers showed a spiral-like,
non-axisymmetric distribution with a systematic velocity gradient. The
line-of-sight velocity field is explained by an infall motion along a parabolic
streamline that falls onto the equatorial plane of the face-on system. The
streamline is quasi-radial and reaches the equatorial plane at a radius of 16
au. This is clearly smaller than that of typical accretion disks in High-Mass
star formation, indicating that the initial angular momentum was very small, or
the CH$_{3}$OH masers selectively trace accreting material that has small
angular momentum. In the former case, the initial specific angular momentum is
estimated to be 8 $\times$ 10$^{20}$ ($M_{*}$$/$10 $M_{\sun}$)$^{0.5}$ cm$^{2}$
s$^{-1}$, or a significant fraction of the initial angular momentum was removed
outside of 100 au. The physical origin of such a streamline is still an open
question and will be constrained by the higher-resolution ($\sim$ 10 mas)
thermal continuum and line observations with ALMA long baselines.
