Discovery of a Cold Extended Condensation in the Orion A Complex

Abstract

The central region of the Orion A cloud complex has been observed in the submillimeter range, using the French balloon-borne 2 m telescope PRONAOS-SPM during its first flight, in 1994 September. An area covering 50' × 10' and including the M42 Nebula has been mapped in four submillimeter photometric bands: λ180-240, 240-340, 340-560, and 560-1050 μm, with high sensitivity (≤2 MJy sr-1) and an angular resolution from 2' to 35. Four brightness enhancements are visible and have been identified with the following sources: (1) the brightest peak corresponding to the central core of the nebula, in the BN/KL source direction; (2) an extended emission region around 5' × 8', to the southeast of BN/KL, correlated with 100 μm IRAS and 13CO emission (this has been identified as a gas-density enhancement associated with a shock region); (3) the edge of an ionized part of the cloud, correlated with the 100 μm emission; and (4) a very cold and extended condensation, discovered at 16' northwest of BN/KL. The emission spectra obtained for these sources show a variation of the dust emissivity spectral index within a large range, from 1 ± 0.1 to 2.2 ± 0.2. The cold condensation discovered (T = 12.5 ± 3 K) has a very low brightness emission, undetected on the 100 μm IRAS map. It extends over approximately 0.7 pc (FWHM), with a total mass of 11 M☉ and a total luminosity of 2.4 L☉.