Mathematics – Logic
Scientific paper
Aug 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984apj...283..486m&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 283, Aug. 15, 1984, p. 486-494. Research supported by the Consiglio Naziona
Mathematics
Logic
75
Cosmic X Rays, Galactic Nuclei, Luminosity, Quasars, Seyfert Galaxies, X Ray Sources, Active Galactic Nuclei, Background Radiation, Big Bang Cosmology, Galactic Evolution, Heao 2, Red Shift, Space Density
Scientific paper
The cosmological evolution and the X-ray luminosity function of quasars and Seyfert galaxies (active galactic nuclei /AGNs/) are derived and discussed. The sample used consists of 56 objects extracted from the expanded Einstein Observatory Medium Sensitivity Survey, and it is exclusively defined by its X-ray properties. The distribution in space of X-ray selected AGNs is confirmed to be strongly nonuniform; the amount of cosmological evolution required by the data is in agreement with a previous determination based on a smaller sample of objects. The X-ray luminosity function (XLF) is derived. The high-luminosity part of the XLF is satisfactorily described by a power law of slope gamma approximately 3.6. A significant flattening is observed at low luminosities. The simultaneous determination of the cosmological evolution and of the X-ray luminosity function of AGNs is then used to estimate the contribution to the extragalactic diffuse X-ray background. Using the best fit values for the evolution of AGNs and for their volume density, it is found that they contribute approximately 80 percent of the 2 keV diffuse X-ray background. Uncertainties in this estimate are still rather large; however, it seems difficult to reconcile the data with a contribution much less than 50 percent.
Gioia Isabella Maria
Maccacaro Tomasso
Stocke John T.
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