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In order to study the temperature distribution of the extended gas within theOrion Kleinmann-Low nebula, we have mapped the emission by methyl cyanide(CH3CN) in its J=6_K-5_K, J=12_K-11_K, J=13_K-12_K, and J=14_K-13_K transitionsat an average angular resolution of ~10 arcsec (22 arcsec for the 6_K-5_Klines), as part of a new 2D line survey of this region using the IRAM 30mtelescope. These fully sampled maps show extended emission from warm gas to thenortheast of IRc2 and the distinct kinematic signatures of the hot core andcompact ridge source components. We have constructed population diagrams forthe four sets of K-ladder emission lines at each position in the maps and havederived rotational excitation temperatures and total beam-averaged columndensities from the fitted slopes. In addition, we have fitted LVG model spectrato the observations to determine best-fit physical parameters at each mapposition, yielding the distribution of kinetic temperatures across the region.The resulting temperature maps reveal a region of hot (T > 350 K) materialsurrounding the northeastern edge of the hot core, whereas the column densitydistribution is more uniform and peaks near the position of IRc2. We attributethis region of hot gas to shock heating caused by the impact of outflowingmaterial from active star formation in the region, as indicated by the presenceof broad CH3CN lines. This scenario is consistent with predictions from C-shockchemical models that suggest that gas-phase methyl cyanide survives in thepost-shock gas and can be somewhat enhanced due to sputtering of grain mantlesin the passing shock front.

Extended warm gas in Orion KL as probed by methyl cyanide