2008/04/04 by Ohad Shemmer, W. N. Brandt, Hagai Netzer +4 · 8 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Black hole (networking) #Eddington luminosity #Galaxies: Formation, Evolution, Phenomena #Galaxy #Luminosity #Optics #Photon #Physics #Spectral index #Spectral line #Spectral slope #astro-ph
paper · pdf · doi:10.1086/588776
13 pages (emulateapj), 6 figures. Accepted for publication in ApJ
arxiv created 2008/04/04 · openalex publication_date 2008/07/20 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We study the hard X-ray spectral properties of 10 highly luminous radio-quiet (RQ) active galactic nuclei (AGNs) at z = 1.3–3.2, including new XMM-Newton observations of four of these sources. We find a significant correlation between the normalized accretion rate ( L / L Edd ) and the hard X-ray photon index (Γ) for 35 moderate- to high-luminosity RQ AGNs, including our 10 highly luminous sources. Within the limits of our sample, we show that a measurement of Γ and L X can provide an estimate of L / L Edd and black hole mass ( M BH ) with a mean uncertainty of a factor of ≲3 on the predicted values of these properties. This may provide a useful probe for tracing the history of BH growth in the universe, utilizing samples of X-ray-selected AGNs for which L / L Edd and M BH have not yet been determined systematically. It may prove to be a useful way to probe BH growth in distant Compton-thin type 2 AGNs. We also find that the optical-X-ray spectral slope (α ox ) depends primarily on optical-UV luminosity rather than on L / L Edd in a sample of RQ AGNs spanning 5 orders of magnitude in luminosity and over 2 orders of magnitude in L / L Edd . We detect a significant Compton-reflection continuum in two of our highly luminous sources, and in the stacked X-ray spectrum of seven other sources with similar luminosities, we obtain a mean relative Compton reflection of R = 0.9 + 0.6 −0.5 and an upper limit on the rest-frame equivalent width of a neutral Fe Kα line of 105 eV. We do not detect a significant steepening of the X-ray power-law spectrum below rest-frame 2 keV in any of our highly luminous sources, suggesting that a soft-excess feature, commonly observed in local AGNs, either does not depend strongly on L / L Edd , or is not accessible at high redshifts using current X-ray detectors.