Distribution of Cold dust in Orion A and B

Abstract

Large scale far-infrared (FIR) observations of the Orion complex at 205 and 138 micron are presented with an aim of studying the distribution of cold (< 25 K) dust. The maps in these FIR bands extend over approximately 3600 sq. arcmin and cover regions around OMC-1, 2, 3 in Orion A and NGC 2023 and NGC 2024 in Orion B. Some limited regions have also been mapped at 57 micron. A total of 15 sources in Orion A and 14 in Orion B (south) have been identified from our FIR maps. Dust temperature distribution in both Orion A and Orion B (south) have been determined reliably using the maps at 205 & 138 micron obtained from simultaneous observations using almost identical beams (1.6 dia). These temperatures have been used to generate map of the optical depth at 150 micron, for the Orion B region. The coldest source detected is in OMC-3 and has a temperature of about 15 K. The diffuse FIR emission in the different sub-regions is found to vary between 25% to 50% of the total FIR emission from that sub-region.