A Joint Deep X-Ray and UV-Excess Survey in Pavo Quasars at Z 1 Contributing to the Extragalactic X-Ray Flux
X-ray selected quasars, with a surface density of ≡32 per square degree, account directly for ≡30% of the all-sky X-ray background in the energy range of the Einstein Observatory. Quasars which were not detected in X-rays may account for a further ≡10% of the X-ray background. No examples have yet been found of any class of sources, other than quasars, which might make a comparable or substantial contribution to the extragalactic X-ray background.
Optical Surveys for Quasars
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