view Abstract Citations (139) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Properties of X-Ray-selected Active Galactic Nuclei. I. Luminosity Function, Cosmological Evolution, and Contribution to the Diffuse X-Ray Background Maccacaro, Tommaso ; della Ceca, Roberto ; Gioia, Isabella M. ; Morris, Simon L. ; Stocke, John T. ; Wolter, Anna Abstract The X-ray luminosity functions (XLF) of X-ray-selected active galactic nuclei (AGNs) and its cosmological evolution are derived and discussed. The sample utilized consists of more than 420 X-ray- selected AGNs extracted from the Einstein Observatory Extended Medium- Sensitivity Survey. The local (z < 0.1) observed XLF as well as the XLF in different redshift shells up to Z ~ 2 have been derived. The local XLF shows a substantial flattening for L_x_ <= 5 x 10^42^ ergs s^-1^ while at higher luminosities it can be approximated by a power law. The AGN XLF obtained in a model-independent way at different redshifts gives direct evidence for cosmological evolution (weak for z <= 0.4 and more pronounced for higher z). The data have been analyzed within the framework of pure luminosity evolution models, and the two most common evolutionary forms L_x_(Z) = L_x_(0)e^cτ^ and L_x_(Z) = L_x_(0)(1 + Z)^c^ have been considered. Best-fit values of 4.18 and 2.56, respectively, have been found for the evolution parameter C. The de-evolved X-ray luminosity function has been derived. A good fit with a broken power law (with slope γ_1_ = 1.35 for L_x_(0) <~ 2.5 x 10^43^ ergs s^-1^ and slope γ_2_ = 3.05 for L_x_(0) >~ 2.5 x 10^43^ ergs s^-1^) has been obtained. There is no evidence for a further slope change outside the range of luminosities sampled (10^42^-10^47^ ergs s^-1^). The simultaneous determination of the cosmological evolution and of the XLF is then used to estimate the contribution of the AGNs 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 ~ 40% of the 2 keV diffuse X-ray background. About 85% of this contribution comes from objects with L_x_(0) between 10^42^ and 10^44^ ergs s^-1^. Publication: The Astrophysical Journal Pub Date: June 1991 DOI: 10.1086/170102 Bibcode: 1991ApJ...374..117M Keywords: Active Galactic Nuclei; Cosmology; Galactic Evolution; Luminosity; X Ray Astronomy; Astronomical Spectroscopy; Background Radiation; Heao 2; Astrophysics; GALAXIES: NUCLEI; GALAXIES: X-RAYS; LUMINOSITY FUNCTION; X-RAYS: SOURCES full text sources ADS | data products NED (427) SIMBAD (21) Related Materials (3) Part 2: 1992ApJ...389..491D Part 3: 1994ApJ...430..533D Part 4: 1996ApJ...465..650D
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Maccacaro et al. (1991) studied this question.