Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986a%26a...161....1d&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 161, no. 1, June 1986, p. 1-6. Research supported by the Ministero della Pubbl
Astronomy and Astrophysics
Astrophysics
26
Active Galactic Nuclei, Cosmology, Galactic Evolution, Quasars, X Ray Sources, Background Radiation, Luminosity, X Ray Spectra
Scientific paper
Based on all the available hard and soft X-ray data, the cosmological evolution of AGNs in the X-ray band is studied. It is shown that an increase in the published soft (0.5-4.5 keV) X-ray fluxes by a factor of about 1.5 is required to bring them into the HEAO-1 flux scale and to remove the apparent mismatching between the HEAO-1 and MSS counts of AGNs. Though the sample of X-ray selected AGNs provided only loose limits on evolutionary models, tight constraints ensue from the observed properties of the X-ray background (XRB). The current picture, that optically selected QSOs have X-ray spectra significantly steeper than the 2-10 keV XRB, is not consistent with the simplest luminosity-dependent density evolutionary models, and would make possible strong luminosity evolution only for high luminosity sources. The MSS luminosity distribution suggests that the transition between nonevolving and evolving sources occurs just close to log Lx of about 43.5.
Danese Lugi
de Zotti Gainfranco
Fasano Giancarmine
Franceschini Alberto
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