Related papers: The peak region of the extragalactic background ra…
Deep X-ray surveys have shown that the cosmic X-ray background (XRB) is largely due to the accretion onto supermassive black holes, integrated over the cosmic time. These surveys have resolved more than 80% of the 0.1-10 keV X-ray…
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)…
While it is understood that the origin of the Cosmic X-ray Background (CXRB) can be explained in terms of a combination of obscured and unobscured AGN, the identity of these obscured AGN showing up in large numbers at faint fluxes remains…
We present the results of calculations of the cosmic AGN background spectrum from 3 keV (4\times 10^{-4} microns) to 1000 microns. These computations make use of the measured X-ray luminosity function and its evolution, as well as fits from…
Active galactic nuclei (AGN) are complex phenomena. At the heart of an AGN is a relativistic accretion disk around a spinning supermassive black hole (SMBH) with an X-ray emitting corona and, sometimes, a relativistic jet. On larger scales,…
The evidence for obscured AGN and in particular for obscured quasars is discussed. The spectrum and source modelling of the X-ray Background suggests that most massive black holes grow by obscured accretion. A possible major growth phase…
The diffuse cosmic X-ray background (CXB) is the sum of the emission of discrete sources, mostly massive black-holes accreting matter in active galactic nuclei (AGN). The CXB spectrum differs from the integration of the spectra of…
The extragalactic background is composed of the emission from all astrophysical sources, both resolved and unresolved, in addition to any diffuse components. In the last decade, there has been significant progress in our understanding of…
We provide a highly concise overview of what X-ray surveys and their multiwavelength follow-up have revealed about the nature of the cosmic X-ray background (CXRB) and its constituent sources. We first describe early global studies of the…
A full understanding of the origin of the hard X-ray background requires a complete and accurate census of the distant galaxies that produce it. Unfortunately, distant X-ray galaxies tend to be very faint at all wavelengths, which hinders…
Our current understanding of the evolution of obscured accretion onto supermassive black holes is reviewed. We consider the literature results on the relation between the fraction of moderately obscured, Compton-thin AGN and redshift, and…
The synthesis model for the cosmic X-ray background (XRB) -based on the integrated emission of Active Galactic Nuclei (AGNs)- is complemented with new observational results. We adopt the most recent estimates of the AGN X-ray luminosity…
We study, by means of dedicated simulations of massive black hole build-up, the possibility to constraint the existence and nature of the AGN population at z>6 with available and planned X-ray and near infrared space telescopes. We find…
In recent years deep X-ray and infrared surveys have provided an efficient way to find accreting supermassive black holes, otherwise known as active galactic nuclei (AGN), in the young universe. Such surveys can, unlike optical surveys,…
Deep field observations are an essential tool to probe the cosmological evolution of galaxies. In this context, X-ray deep fields provide information about some of the most energetic cosmological objects: active galactic nuclei (AGN).…
Large extragalactic surveys allow us to trace, in a statistical sense, how supermassive black holes, their host galaxies, and their dark matter halos evolve together over cosmic time, and so explore the consequences of AGN feedback on…
Extragalactic X-ray surveys are exceptionally powerful tools for studying the evolution of supermassive black holes and their host galaxies, by detecting large numbers of active galactic nuclei (AGN) and star-forming galaxies over a wide…
The inner 20 gravitational radii around the black hole at the centre of luminous Active Galactic Nuclei and stellar mass Black Hole Binaries are now being routinely mapped by X-ray spectral-timing techniques. Spectral blurring and…
Current X-ray surveys have proved to be essential tools in order to identify and study AGNs across cosmic time. However, there is evidence that the most heavily obscured AGNs are largely missing even in the deepest surveys. The search for…
The spectrum of the hard X-ray background records the history of accretion processes integrated over the cosmic time. Several observational and theoretical evidences indicate that a significant fraction of the energy density is obscured by…