Aims. The aim of this work is to characterize the average Fe K emission properties of active galactic nuclei (AGNs) in the source rest-frame. Methods. We selected a sample of 248 AGNs from the 2XMM catalog, covering a wide redshift range 0 < z < 5 and with the EPIC-PN net 2-10 keV rest-frame counts ≥200 and power law photon indices in the range 1.5-2.2. We employed two fully independent restframe stacking procedures to compute the mean Fe K profile. The counting statistics for the integrated spectrum is comparable to the one available for the best studied local Seyferts. To identify the artifacts possibly introduced by the stacking procedure, we have carried out simulations. Results. We report that the average Fe K line profile in our sample is best represented by a combination of a narrow and a broad line. The equivalent widths of the narrow and broad (parametrized with a diskline) components are ∼30 eV and ∼100 eV, respectively. We also discuss the results of more complex fits and the implications of the adopted continuum modeling on the broad line parameters and its detection significance.
Aims. Our analysis is aimed at characterizing the properties of the integrated spectrum of active galactic nuclei (AGNs), such as the ubiquity of the Fe Kα emission in AGNs and the dependence of the spectral parameters on the X-ray luminosity and redshift. Methods. We selected 2646 point sources from the 2XMM catalog at high galactic latitude (|BII| > 25 degrees) and with the sum of EPIC-PN and EPIC-MOS 0.2-12 keV counts greater than 1000. Redshifts were obtained for 916 sources from the Nasa's Extragalactic Database. We excluded sources classified as HII regions, groups/clusters, star-forming/starburst galaxies. The final sample consists of 507 AGN. Individual source spectra were summed in the observed frame to compute the integrated spectra in different redshift and luminosity bins over the range 0 < z < 5. Detailed analysis of these spectra used appropriately normalized background spectra and exposure time-weighted response and ancillary files. Results. We find that the narrow Fe Kα line at 6.4 keV is significantly detected up to z = 1. The line equivalent width decreases with increasing X-ray luminosity in the 2-10 keV band ("Iwasawa-Taniguchi effect"). The anticorrelation is characterized by the relation log(EW Fe ) = (1.66 ± 0.09) + (−0.43 ± 0.07) log(L X,44 ), where EW Fe is the rest frame equivalent width of the neutral iron Kα line in eV and L X,44 is the 2-10 keV X-ray luminosity in units of 10 44 erg s −1 . The equivalent width is nearly independent of redshift up to z ∼ 0.8 with an average value of 101 ± 40 (rms dispersion) eV in the luminosity range 43.5 ≤ log L X ≤ 44.5. Our analysis also confirms the hardening of the spectral indices at low luminosities, implying a dependence of obscuration on luminosity. Conclusions. We confirm that the neutral narrow Fe Kα line is an almost ubiquitous feature of AGNs. We find compelling evidence supporting the "Iwasawa-Taniguchi effect" over a redshift interval larger than probed in any previous study. We detect no evolution of the average rest frame equivalent width of the Fe Kα line with redshift.
We exploited the 2XMM catalog and archival products to investigate the properties of the Fe Kα line at different redshifts. Individual source spectra are stacked in different redshift and luminosity bins over the range 0
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