Emission Nebulae as Radio Sources

Abstract

Attempts have been made to detect 14 bright emission nebulae at a wavelength of 3?5 m using a pencil-beam radio telescope with a beamwidth of 50 min of arc. Of these nebulae, six were probably observed in emission, seven were undetectable, and one, NGC 6357, was observed in absorption; radio isophotes were obtained for NGC 2237 and NGC 3372. Radio and optical data have been combined to estimate electron densities, masses, and sometimes the electron temperature of many of the nebulae. Values range from an electron density of 3 cm?3 and a mass of 3×10. solar masses for the outer regions of the 30 Doradus complex to an average electron density of 500 cm?3 and a mass of 20 solar masses for the Orion Nebula. Temperatures generally appear to be in the neighbourhood of 10,000 °K, except in the case of NGC 6357, for which 6500 °K is estimated.