Nature 290, 483 - 485 (09 April 1981); doi:10.1038/290483a0

Precursor active galaxies and the cosmic X-ray background

Elihu Boldt & Darryl Leiter

Laboratory for High Energy Astrophysics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

Data on the isotropic extragalactic X-ray background (>3 keV) obtained with the HEAO 1 A2 instrument¹ yield a spectrum over the energy band of maximum flux that is well described by a thermal model involving an optically thin hot plasma at a temperature of a half-billion degrees (kT = 405 keV). The spectra for known strong X-ray sources in the present epoch (active galaxies, clusters of galaxies) obtained with the same HEAO 1 instrument^2,3 indicate that such objects at high redshifts cannot account for most of this background. On the other hand, deep-field exposures to soft X rays (<3 keV) with the HEAO 2 Einstein Observatory⁴ suggest that discrete sources could be a sufficient explanation. This implies either (1) that these dim sources are generally unrelated to relatively bright nearby objects or (2) that they represent an earlier stage in their evolution. Short-lived thermal X-ray emission by galactic winds peculiar to an earlier epoch has been suggested⁵ as an explanation of the first kind, but the need for postulating new sources can be obviated if, as Leiter has argued⁶, prolific X-ray sources evolve in connection with active galactic nuclei involving massive compact objects. Here, we pursue the suggestion by Carr⁷ that most of the cosmic X-ray background (CXB) arises from thermal X-ray emission associated with black hole accretion disks for compact objects formed before galaxies but we favour a model where the onset of significant X-rays takes place within the epoch of galaxy formation at z4, when accretion disks are created by the interaction between massive black holes of pregalactic origin and young galaxies.

References

1.	Marshall, F. et al. Astrophys. J. 235, 4 (1980). | Article | ISI | ChemPort |
2.	Boldt, E. Bull. Am. Ass. Sci. 11, 651 (1979).
3.	Boldt, E. Comments Astrophys. (in the press).
4.	Giacconi, R. et al. Astrophys. J. Lett. 234, L1 (1979). | Article |
5.	Bookbinder, J., Cowie, I., Krolik, J., Ostriker, J. & Rees, M. Astrophys. J. 237, 647 (1980). | Article | ISI | ChemPort |
6.	Leiter, D. Astr. Astrophys. 89, 370 (1980). | ISI | ChemPort |
7.	Carr, B. J. Nature 284, 326 (1980). | ISI | ChemPort |
8.	Bignami, G., Fichtel, C., Hartman, R. & Thompson, D. Astrophys. J. 232, 649 (1979). | Article | ISI | ChemPort |
9.	Fichtel, C. & Trombka, J. Gamma-Ray Astrophysics, New Insights into the Universe Ch. 9 (NASA-R. P.-007 in the press).
10.	Wills, D. Phys. Scr. 17, 333 (1978). | ISI |
11.	Murray, S. Bull. Am. Ass. Sci. 11, 642 (1979).
12.	Bahcall, J. N. & Soneira, R. M. Astrophys. J. Lett. 238, L17 (1979). | Article |
13.	Payne, D. & Eardley, D. Astrophys. Lett. 19, 39 (1977). | ISI | ChemPort |
14.	Shapiro, S., Lightman, A. & Eardley, D. Astrophys. J. 204, 187 (1976). | Article | ISI |
15.	Liang, E. P. T. Astrophys. J. 234, 1105 (1980). | Article | ISI |
16.	Brinkmann, W. Astr. Astrophys. 85, 146 (1980). | ISI | ChemPort |
17.	Ruffini, R. & Wheeler, J. in Neutron Stars Black Holes and Binary X-Ray Sources (eds Gursky, H. & Ruffini, R. ) 389 (Reidel, Dordrecht, 1975).
18.	Thorne, K. Astrophys. J. 191, 507 (1974). | Article | ISI |
19.	Leiter, D. & Kafatos, M. in Proc. La Jolla Institute Workshop on Particle Acceleration Mechanisms in Astrophysics, 419 (American Institute of Physics, New York, 1979). | ChemPort |
20.	Piran, T., Shaham, J. & Katz, J. Astrophys. J. Lett. 196, L107 (1975). | Article | ChemPort |
21.	Blandford, R. D. in Active Galactic Nuclei (eds Hazard, C. & Mitton, S) 241 (Cambridge University Press, 1979).
22.	Lovelace, R., MacAuslan, J. & Burns, M. in Proc. La Jolla Institute Workshop on Particle Acceleration Mechanisms in Astrophysics 399 (American Institute of Physics, New York, 1979). | ChemPort |
23.	Vestrand, W., Scott, J., Marsher, A. & Christiansen, W. Astrophys. J. 245 (in the press).
24.	Cavaliere, A. & Morrison, P. Astrophys. J. Lett. 238, L63 (1980). | Article | ChemPort |
25.	Simkin, S., Su, H. & Schwarz, M. Astrophys. J. 237, 404 (1980). | Article | ISI | ChemPort |
26.	Bardeen, J. in Black Holes (eds DeWitt, C. & B. S.) 225 (Gordon and Breach, New York 1973).
27.	Boldt, E. Bull. Am. Ass. Sci. 12, 495 (1980).Leiter, D. Bull. Am. Ass. Sci. 12, 496 (1980).
28.	Jones, T. Astrophys. J. 233, 796 (1979). | Article | ISI | ChemPort |
29.	Worrall, D. et al. Astrophys. J. 232, 683 (1979). | Article | ISI | ChemPort |
30.	Worrall, D., Boldt, E., Holt, S. & Serlemitsos, P. Astrophys. J. 240, 421 (1980). | Article | ISI | ChemPort |
31.	Marshall, N., Warwick, R. S. & Pounds, K. A. Mon. Not. R. astr. Soc. (submitted).
32.	Grindlay, J., Steiner, J., Forman, W., Canizares, C. & McClintock, J. Astrophys. J. Lett. 239, L43 (1980). | Article | ChemPort |
33.	Kafatos, M. & Leiter, D. Astrophys. J. 229, 46 (1979). | Article | ISI | ChemPort |