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21-cm Absorption in BL Lac

Published online by Cambridge University Press:  14 August 2015

M. H. Cohen
M. H. Cohen*
Affiliation:
California Institute of Technology, Pasadena, Calif., U.S.A.

Abstract

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Observations with the Owens Valley Radio Observatory interferometer show that BL Lac has a 21-cm hydrogen absorption line, produced by a local intervening cloud. The line is centered on zero velocity (LSR), has a width of about 5 km s−1, and shows an optical depth of 0.5. BL Lac is at galactic latitude b= −10°. No firm distance limit is possible, but such clouds are, typically, 100 pc apart. This observation is consistent with BL Lac being an extragalactic object. Other observations leading to a similar conclusion are of rotation measure (MacLeod and Andrew, 1968) and of reddening (Bertaud et al., 1969).

Type
Abstract
Information
Symposium - International Astronomical Union , Volume 44: External Galaxies and Quasi-Stellar Objects , 1972 , pp. 271
Copyright
Copyright © Reidel 1972 

References

Bertaud, Ch., Dumortier, B., Véron, P., Wlérick, G., Adam, G., Bigay, J., and Garnier, R.: 1969, Astron. Astrophys. 3, 436.Google Scholar
MacLeod, J. M. and Andrew, B. H.: 1968, Astrophys. Letters 1, 243.Google Scholar