Aperture synthesis of interstellar neutral hydrogen in absorption. II. Cygnus A, the Crab Nebula, and other sources

Journal Article · Sat Sep 01 04:00:00 EDT 1973 · Astrophys. J., v. 184, no. 2, pp. 379-396

OSTI ID:4343008

Greisen, E W

The Owens Valley Radio Observatory interferometer has been used to carry out a program of aperture synthesis in the interstellar neutral hydrogen line. In a previous paper, the observing and reduction techniques and the results on the Perseus arm feature of Cassiopeia A were discussed. In the present paper, the results of synthesis observations of Cygnus A, the Crab Nebula, and 3C 353 and single-spacing observations of W12 and 3C 147 are presented. Again, 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 100 cm/sup -3/. Upper limits to the temperatures lower than 50 deg K are found for some spectral components, but upper limits between 80 deg and 160 deg K are more common. The implications of these results for the two-phase model of the interstellar medium are discussed. In particular, earlier claims of the unambiguous detection of the hot intercloud medium are found to be unwarranted. The data for the Crab Nebula and 3C 147 suggest that density-wave shock fronts are not maintained as far from the plane of the Galaxy as 175 pc. The results for Cygnus A are interpreted as indicating a shell of hydrogen expanding at 2 km s/sup -1/ with an outer radius of about 9.7 pc and a total mass of around 175 solar masses. (auth)

• Research Organization: California Institute of Technology
• NSA Number: NSA-29-022044
• OSTI ID: 4343008
• Journal Information: Astrophys. J., v. 184, no. 2, pp. 379-396, Journal Name: Astrophys. J., v. 184, no. 2, pp. 379-396; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

*COSMIC RADIO SOURCES-- HYDROGEN
*MILKY WAY-- INTERSTELLAR SPACE
*SUPERNOVA REMNANTS-- INTERFEROMETRY
ABSORPTION
CRAB NEBULA
GALAXIES
N56500* --Physics (Astrophysics & Cosmology)--Galaxies
NEBULAE
PULSARS
RADIOWAVE RADIATION
VELOCITY