Spatially Resolving Substructures within the Massive Envelope around an
  Intermediate-mass Protostar: MMS 6/OMC-3
  With the Submillimeter Array, the brightest (sub)millimeter continuum source
in the OMC-2/3 region, MMS 6, has been observed in the 850 um continuum
emission with approximately 10 times better angular resolution than previous
studies (~0.3"; ~120 AU at Orion). The deconvolved size, the mass, and the
column density of MMS 6-main are estimated to be 0.32"x0.29" (132 AUx120 AU),
0.29 Mo, and 2.1x10^{25} cm^{-2}, respectively. The estimated extremely high
mean number density, 1.5x10^{10} cm^{-3}, suggests that MMS 6-main is likely
optically thick at 850 um. We compare our observational data with three
theoretical core models: prestellar core, protostellar core + disk-like
structure, and first adiabatic core. These comparisons clearly show that the
observational data cannot be modeled as a simple prestellar core with a gas
temperature of 20 K. A self-luminous source is necessary to explain the
observed flux density in the (sub)millimeter wavelengths. Our recent detection
of a very compact and energetic outflow in the CO (3-2) and HCN (4-3) lines,
supports the presence of a protostar. We suggest that MMS 6 is one of the first
cases of an intermediate mass protostellar core at an extremely young stage. In
addition to the MMS 6-main peak, we have also spatially resolved a number of
spiky structures and sub-clumps, distributed over the central 1000 AU. The
masses of these sub-clumps are estimated to be 0.066-0.073 Mo, which are on the
order of brown dwarf masses. Higher angular resolution and higher sensitivity
observations with ALMA and EVLA will reveal the origin and nature of these
structures such as whether they are originated from fragmentations, spiral
arms, or inhomogeneity within the disk-like structures/envelope.
