Prospects for X-Ray Observations of Cosmological Significance
The cosmic X-ray background (at least in the energy band ~2–10 keV) shares with the microwave background the property of originating at a high redshift (Z×~ 1–5; Zm~103). Thus, studies of the structure, spectrum and origin of the X-ray background are potentially important cosmologically. Existing measurements of the background isotropy and deductions made therefrom are reviewed and seen to provide interesting limits on the matter distribution on scales larger than that of super-clusters. Source counts from the Einstein Observatory and earlier sky survey experiments show a significant (and possibly dominant) component of the X-ray background to arise from a strongly evolving population of high redshift QSO’s. However, the present X-ray data do not yield definitive cosmological data, and it is concluded that the realisation of this potential must await the deep all-sky survey of ROSAT (in~1987) and, more particularly, the 1.2 metre AXAF X-ray telescope (~1990?) with its capability to study many types of X-ray source to redshifts z≥1.
KeywordsCosmic Microwave Background High Redshift Luminosity Function Luminosity Distance Extragalactic Source
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