Wide-Area Mapping of 155 Micron Continuum Emission from the Orion Molecular Cloud Complex

We present the results of a wide-area mapping of the far-infrared continuumemission toward the Orion complex by using a Japanese balloon-borne telescope.The 155-um continuum emission was detected over a region of 1.5 deg^2 aroundthe KL nebula with 3' resolution similar to that of the IRAS 100-um map.Assuming a single-temperature model of the thermal equilibrium dust, maps ofthe temperature and the optical depth were derived from the 155 um intensityand the IRAS 100 um intensity. The derived dust temperature is 5 - 15 K lowerand the derived dust optical thickness were derived from the 155-um intensityand the IRAS 100-um intensity. The derived dust temperature is 5 - 15 K lowerand the derived dust optical depth is 5 - 300 times larger than those derivedfrom the IRAS 60 and 100-um intensities due to the significant contribution ofthe statistically heated very small grains to the IRAS 60-um intensity. Theoptical-thickness distribution shows a filamentary dust ridge that has a 1.5degrees extent in the north - south direction and well resembles theIntegral-Shaped Filament (ISF) molecular gas distribution. The gas-to-dustratio derived from the CO molecular gas distribution along the ISF is in therange 30 - 200, which may be interpreted as being an effect of CO depletion dueto the photodissociation and/or the freezing on dust grains.Comment: 23 pages, 7 figures, 1 table, to appear in PASJ, Vol. 56, No.