We mapped the kinetic temperature structure of the Orion molecular cloud 1 ( OMC-1 ) with para-H _ { 2 } CO ( J _ { K _ { a } K _ { c } } = 3 _ { 03 } –2 _ { 02 } , 3 _ { 22 } –2 _ { 21 } , and 3 _ { 21 } –2 _ { 20 } ) using the APEX 12 m telescope .
This is compared with the temperatures derived from the ratio of the NH _ { 3 } ( 2,2 ) / ( 1,1 ) inversion lines and the dust emission .
Using the RADEX non-LTE model , we derive the gas kinetic temperature modeling the measured averaged line ratios of para-H _ { 2 } CO 3 _ { 22 } –2 _ { 21 } /3 _ { 03 } –2 _ { 02 } and 3 _ { 21 } –2 _ { 20 } /3 _ { 03 } –2 _ { 02 } .
The gas kinetic temperatures derived from the para-H _ { 2 } CO line ratios are warm , ranging from 30 to ¿200 K with an average of 62 \pm 2 K at a spatial density of 10 ^ { 5 } cm ^ { -3 } .
These temperatures are higher than those obtained from NH _ { 3 } ( 2,2 ) / ( 1,1 ) and CH _ { 3 } CCH ( 6–5 ) in the OMC-1 region .
The gas kinetic temperatures derived from para-H _ { 2 } CO agree with those obtained from warm dust components measured in the mid infrared ( MIR ) , which indicates that the para-H _ { 2 } CO ( 3–2 ) ratios trace dense and warm gas .
The cold dust components measured in the far infrared ( FIR ) are consistent with those measured with NH _ { 3 } ( 2,2 ) / ( 1,1 ) and the CH _ { 3 } CCH ( 6–5 ) line series .
With dust at MIR wavelengths and para-H _ { 2 } CO ( 3–2 ) on one side and dust at FIR wavelengths , NH _ { 3 } ( 2,2 ) / ( 1,1 ) , and CH _ { 3 } CCH ( 6–5 ) on the other , dust and gas temperatures appear to be equivalent in the dense gas ( n ( H _ { 2 } ) \gtrsim 10 ^ { 4 } cm ^ { -3 } ) of the OMC-1 region , but provide a bimodal distribution , one more directly related to star formation than the other .
The non-thermal velocity dispersions of para-H _ { 2 } CO are positively correlated with the gas kinetic temperatures in regions of strong non-thermal motion ( Mach number \gtrsim 2.5 ) of the OMC-1 , implying that the higher temperature traced by para-H _ { 2 } CO is related to turbulence on a \sim 0.06 pc scale .
Combining the temperature measurements with para-H _ { 2 } CO and NH _ { 3 } ( 2,2 ) / ( 1,1 ) line ratios , we find direct evidence for the dense gas along the northern part of the OMC-1 10 km s ^ { -1 } filament heated by radiation from the central Orion nebula .