Massive Quiescent Cores in Orion: Dynamical State Revealed by
  High-Resolution Ammonia Maps
  We present combined VLA and Green Bank Telescope images of \ammonia\
inversion transitions (1,1) and (2,2) toward OMC2 and OMC3. We focus on the
relatively quiescent Orion cores, which are away from the Trapezium cluster and
have no sign of massive protostars nor evolved star formation, such as IRAS
source, water maser, and methanol maser. The 5\arcsec\ angular resolution and
$0.6 \rm{}km\,s^{-1}$ velocity resolution of these data enable us to study the
thermal and dynamic state of these cores at $\sim{}0.02 \rm{}pc$ scales,
comparable to or smaller than those of the current dust continuum surveys. We
measure temperatures for a total of 30 cores, with average masses of $11\,\Ms$,
radii of $0.039 \rm{}pc$, virial mass ratio $\bar{R_{vir}}$ = 3.9, and critical
mass ratio $\bar{R_{C}}$ = 1.5. Twelve sources contain \textit{Spitzer}
protostars. The thus defined starless and protostellar subsamples have similar
temperature, line width, but different masses, with an average of $7.3\,\Ms$
for the former and $16\,\Ms$ for the latter. Compared to others Gould Belt
dense cores, mores Orion cores have a high gravitational-to kinetic energy
ratio and more cores have a larger thant unity critical mass ratio. Orion dense
cores have velocity dispersion similar to those of cores in low-mass
star-forming regions but larger masses for fiven size. Some cores appear to
have truly supercritical gravitational-to-kinetic energy ratios, even when
considering significant observational uncertainties: thermal and non-thermal
gas mothins alone cannot prevent collapse.
