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Aperture Synthesis of Interstellar Neutral Hydrogen in Absorption. II. Cygnus A, the Crab Nebula, and Other Sources,
OWENS VALLEY RADIO OBSERVATORY PASADENA CALIF
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The Owens Valley Radio Observatory interferometer has been used to carry out a program of aperture synthesis in the interstellar neutral hydrogen line. The results of synthesis observations of Cygnus A, the Crab Nebula and 3C353 and single-spacing observations of W12 and 3C147 are presented. Considerable spatial structure in the absorbing medium is found with scale lengths about 1 pc and perhaps even as small as 0.14 pc being common. Some of the small-scale features are seen as condensations within much larger clouds. The hydrogen densities appear to be mostly on the order of 100cc. Upper limits to the temperatures lower than 50K are found for some spectral components, but upper limits between 80 and 160K are more common. The implications of these results for the two-phase model of the interstellar medium are discussed. Author Modified Abstract
APPROVED FOR PUBLIC RELEASE