90 GHz AND 150 GHz OBSERVATIONS OF THE ORION M42 REGION. A SUBMILLIMETER TO RADIO ANALYSIS

Abstract

We have used the new 90 GHz MUSTANG camera on the Robert C. Byrd Green Bank Telescope (GBT) to map the bright Huygens region of the star-forming region M42 with a resolution of 9'' and a sensitivity of 2.8 mJy beam−1. Ninety GHz is an interesting transition frequency, as MUSTANG detects both the free–free emission characteristic of the H ii region created by the Trapezium stars, normally seen at lower frequencies, and thermal dust emission from the background OMC1 molecular cloud, normally mapped at higher frequencies. We also present similar data from the 150 GHz GISMO camera taken on the IRAM 30 m telescope. This map has 15'' resolution. By combining the MUSTANG data with 1.4, 8, and 21 GHz radio data from the VLA and GBT, we derive a new estimate of the emission measure averaged electron temperature of Te = 11376 ± 1050 K by an original method relating free–free emission intensities at optically thin and optically thick frequencies. Combining Infrared Space Observatory–long wavelength spectrometer (ISO–LWS) data with our data, we derive a new estimate of the dust temperature and spectral emissivity index within the 80'' ISO–LWS beam toward Orion KL/BN, Td = 42 ± 3 K and βd = 1.3 ± 0.1. We show that both Td and βd decrease when going from the H ii region and excited OMC1 interface to the denser UV shielded part of OMC1 (Orion KL/BN, Orion S). With a model consisting of only free–free and thermal dust emission, we are able to fit data taken at frequencies from 1.5 GHz to 854 GHz (350 μm).