1. Gunn, J. E. and Peterson B. A.; 1965, Astrophys. J.
142, 1633.
2. Noerdlinger, P. D.; 1969, Astrophys. J.
156, 841.
3. Rees, M. J. and Setti, G.; 1969, Astron. Astrophys. (submitted for publication).
4. Sunyaev, R. A.; 1969, Astrophys. Letters
3, 33.