The Massive Protostellar Cluster NGC6334I at 220 AU Resolution:
  Discovery of Further Multiplicity, Diversity and a Hot Multi-Core
  We present VLA and ALMA imaging of the deeply-embedded protostellar cluster
NGC6334I from 5 cm to 1.3 mm at angular resolutions as fine as 0.17 (220 AU).
The dominant hot core MM1 is resolved into seven components at 1.3 mm,
clustered within a radius of 1000 AU. Four of the components have brightness
temperatures >200 K, radii ~300 AU, minimum luminosities ~10000 Lsun, and must
be centrally heated. We term this new phenomenon a "hot multi-core". Two of
these objects also exhibit compact free-free emission at longer wavelengths,
consistent with a hypercompact HII region (MM1B) and a jet (MM1D). The spatial
kinematics of the water maser emission centered on MM1D are consistent with it
being the origin of the high-velocity bipolar molecular outflow seen in CO. The
close proximity of MM1B and MM1D (440~AU) suggests a proto-binary or a
transient bound system. Several components of MM1 exhibit steep millimeter SEDs
indicative of either unusual dust spectral properties or time variability. In
addition to resolving MM1 and the other hot core (MM2) into multiple
components, we detect five new millimeter and two new centimeter sources. Water
masers are detected for the first time toward MM4A, confirming its membership
in the protocluster. With a 1.3 mm brightness temperature of 97 K coupled with
a lack of thermal molecular line emission, MM4A appears to be a highly
optically-thick 240 Lsun dust core, possibly tracing a transient stage of
massive protostellar evolution. The nature of the strongest water maser source
CM2 remains unclear due to its combination of non-thermal radio continuum and
lack of dust emission.
