We present combined VLA and Green Bank Telescope images of NH _ { 3 } 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 ^ { \prime \prime } angular resolution and 0.6 ~ { } { } km s ^ { -1 } velocity resolution of these data enable us to study the thermal and dynamic state of these cores at \sim { } 0.02 ~ { } { } 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 { { } M } _ { \odot } , radii of 0.039 ~ { } { } pc , virial mass ratio \overline { R _ { vir } } = 3.9 , and critical mass ratio \overline { R _ { C } } = 1.5 .
Twelve sources contain Spitzer protostars .
The thus defined starless and protostellar subsamples have similar temperature , line width , but different masses , with an average of 7.3 { { } M } _ { \odot } for the former and 16 { { } M } _ { \odot } 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 can not prevent collapse .