Quasar Evolution and Luminosity Function: An X-Ray Perspective

  • Yoram Avni
Part of the Astrophysics and Space Science Library book series (ASSL, volume 121)


X-ray properties of optically-selected QSOs are reviewed, and their implications for the QSO evolution and luminosity function are summarized. Analyses of the explicit dependence of αo,x, the x-ray to optical luminosity ratio parameter, on redshift z and optical luminosity Lo, are described. In particular, results from a recent analysis of complete, magnitude-limited samples of optically-selected QSOs are presented. Previous results obtained from the study of heterogeneous samples are confirmed. It is shown that the large majority, probably all, of optically-selected QSOs are x-ray loud: no more than a few precent can be x-ray quiet. Thus, x-ray emission seems to be a universal property of QSOs. It is found that comparisons of the optical evolution and luminosity function, combined with the αo,x(z,Lo) dependence, with x-ray-selected samples, are numerically sensitive to the details of the input ingredients. There is a residual discrepancy of about a factor of two between the QSO x-ray number counts calculated from available simple pure luminosity evolution models for the optical evolution and luminosity function combined with the best estimate αo,x(z,Lo) dependence, and observed counts from x-ray selected samples. Directions for further research, which will contribute to our understanding of the full bivariate optical-x-ray evolution and luminosity function, are discussed.


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Copyright information

© Springer Science+Business Media Dordrecht 1986

Authors and Affiliations

  • Yoram Avni
    • 1
    • 2
  1. 1.Harvard-Smithsonian Center for AstrophysicsCambridgeUSA
  2. 2.Weizmann Institute of ScienceRehovotIsrael

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