Related papers: A physical model for the hard X-ray background
The cosmic X-ray background (XRB) spectrum and active galaxy number counts encode essential information about the spectral evolution of active galactic nuclei (AGNs) and have been successfully modeled by XRB synthesis models for many years.…
Chandra and XMM-Newton have resolved the 2-8 keV X-ray Background (XRB) into point sources. Many of the fainter sources are obscured active galactic nuclei (AGN) with column densities in the range of 10^22-10^23 pcmsq, some of which have…
The integrated emission of highly obscured AGN is expected to provide a major contribution to the X-ray energy density in the Universe: the X-ray background (XRB). The study of these objects is possible only at energies where the effects of…
The growth of supermassive black holes across cosmic time leaves a radiative imprint recorded in the X-ray background (XRB). The XRB spectral shape suggests that a large population of distant, hidden nuclei must exist, which are now being…
Recent Chandra and XMM-Newton surveys have uncovered a large fraction of the obscured AGN responsible of the hard X-ray background. One of the most intriguing results of extensive programs of follow-up observations concerns the optical and…
Highly obscured active galactic nuclei (AGN) are common in nearby galaxies, but are difficult to observe beyond the local Universe, where they are expected to significantly contribute to the black hole accretion rate density. Furthermore,…
Recent work by Risaliti et al.(1999) suggests that more than half of all Seyfert 2 galaxies in the local universe are Compton-thick (N_H > 10^24 cm^-2). This has implications for AGN synthesis models for the X-ray background (XRB), the…
X-ray luminosity functions (XLFs) of Active Galactic Nuclei (AGN) trace the growth and evolution of supermassive black hole populations across cosmic time, however, current XLF models are poorly constrained at redshifts of z>6, with a lack…
We investigate the cosmological evolution of the hard X-ray luminosity function (HXLF) of Active Galactic Nuclei (AGN) in the 2-10 keV luminosity range of 10^{41.5} - 10^{46.5} erg s^-1 as a function of redshift up to 3. From a combination…
Accretion and ejection of matter in active galactic nuclei (AGN) are tightly connected phenomena and represent fundamental mechanisms regulating the growth of the central supermassive black hole and the evolution of the host galaxy.…
The evolution of the luminosity function (LF) of Active Galactic Nuclei (AGNs) at $z \gtrsim 5$ represents a key constraint to understand their contribution to the ionizing photon budget necessary to trigger the last phase transition in the…
We analyse the ROSAT PSPC hardness ratio and the 0.5-2 keV to 2-10 keV flux ratio of 65 Active Galactic Nuclei (AGN) for which there are both ROSAT archival observations available and 2-10 keV fluxes, mostly from the HEAO-1 MC-LASS survey.…
Heavily obscured accretion is believed to represent an important stage in the growth of supermassive black holes, and to play an important role in shaping the observed spectrum of the Cosmic X-ray Background (CXB). Hard X-ray (E$>$10 keV)…
Accretion disks of active galactic nuclei (AGN) have been proposed as promising sites for producing both (stellar-mass) compact object mergers and extreme mass ratio inspirals. Along with the disk-assisted migration/evolution process,…
The origin of the hard X-ray background (XRB) as a superposition of unabsorbed and absorbed Active Galactic Nuclei is now widely accepted as the standard model. The identification of faint X-ray sources in ROSAT, ASCA, and BeppoSAX…
We revisit black hole mass estimates for high-redshift broad-line active galactic nuclei (AGNs) discovered with JWST by jointly analysing their broad emission lines and their systematic non-detections in deep Chandra imaging. Building upon…
We investigate the Eddington ratio distribution of X-ray selected broad-line active galactic nuclei (AGN) in the redshift range 1.0<z<2.2, where the number density of AGNs peaks. Combining the optical and Subaru/FMOS near-infrared…
A bright, soft X-ray source was detected on 2010 July 14 during an XMM--Newton slew at a position consistent with the galaxy GSN 069 (z=0.018). Previous ROSAT observations failed to detect the source and imply that GSN 069 is now >240 times…
We investigate the role of host galaxy classification and black hole mass in a heterogeneous sample of 276 mostly nearby (z<0.1) X-ray and IR selected AGN. Around 90% of Seyfert 1 AGN in bulge-dominated host galaxies (without disk…
The co-evolution of host galaxies and the active black holes which reside in their centre is one of the most important topics in modern observational cosmology. Here we present a study of the properties of obscured Active Galactic Nuclei…