Distribution of cold dust in Orion A and B

Abstract

Large-scale far-infrared (FIR) observations of the Orion complex at 205 and 138 µm are presented with the aim of studying the distribution of cold (<25 K) dust. The maps in these FIR bands extend over ~3600 arcmin² and cover regions around OMC-1, 2, and 3 in Orion A and NGC 2023 and NGC 2024 in Orion B. Some limited regions have also been mapped at 57 µm. 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 and 138 µm obtained from simultaneous observations using almost identical beams (16 diameter). These temperatures have been used to generate the map of τ₁₅₀, the optical depth at 150 µm, for the Orion B region. The coldest source detected is in OMC-3 and has temperature ~15 K. The diffuse FIR emission in the different subregions is found to vary between 25% and 50% of the total FIR emission from that subregion.