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We mapped the kinetic temperature structure of the Orion molecular cloud 1with para-H2CO(303-202, 322-221, and 321-220) using the APEX 12m telescope.This is compared with the temperatures derived from the ratio of theNH3(2,2)/(1,1) inversion lines and the dust emission. Using the RADEX non-LTEmodel, we derive the gas kinetic temperature modeling the measured averagedline ratios of para-H2CO 322-221/303-202 and 321-220/303-202. The gas kinetictemperatures derived from the para-H2CO line ratios are warm, ranging from 30to >200 K with an average of 62 K at a spatial density of 10$^5$ cm$^{-3}$.These temperatures are higher than those obtained from NH3(2,2)/(1,1) andCH3CCH(6-5) in the OMC-1 region. The gas kinetic temperatures derived frompara-H2CO agree with those obtained from warm dust components measured in themid infrared (MIR), which indicates that the para-H2CO(3-2) ratios trace denseand warm gas. The cold dust components measured in the far infrared (FIR) areconsistent with those measured with NH3(2,2)/(1,1) and the CH3CCH(6-5) lineseries. With dust at MIR wavelengths and para-H2CO(3-2) on one side and dust atFIR wavelengths, NH3(2,2)/(1,1), and CH3CCH(6-5) on the other, dust and gastemperatures appear to be equivalent in the dense gas of the OMC-1 region, butprovide a bimodal distribution, one more directly related to star formationthan the other. The non-thermal velocity dispersions of para-H2CO arepositively correlated with the gas kinetic temperatures in regions of strongnon-thermal motion (Mach number >2.5) of the OMC-1, implying that the highertemperature traced by para-H2CO is related to turbulence on a 0.06 pc scale.Combining the temperature measurements with para-H2CO and NH3(2,2)/(1,1) lineratios, we find direct evidence for the dense gas along the northern part ofthe OMC-1 10 km s$^{-1}$ filament heated by radiation from the central Orionnebula.

Kinetic temperature of massive star-forming molecular clumps measured with formaldehyde. III. The Orion Molecular Cloud 1