Related papers: On the Contribution of Active Galactic Nuclei to t…
It is a widespread opinion that hydrogen reionization is mainly driven by primeval star-forming galaxies, with a minor role of high-z active galactic nuclei. Recent observations, however, challenge this notion, indicating a number of issues…
We use hydrodynamic simulations post-processed with the radiative-transfer code RADAMESH to assess recent claims that the low HeII opacity observed in z>3 quasar spectra may be incompatible with models of HeII reionization driven by the…
The observed scatter in intergalactic Lyman-$\alpha$ opacity at $z \lesssim 6$ requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that…
Reionization marks one of the most important phase transitions in the history of the Universe, during which neutral baryonic matter was transformed into ionized plasma. While star-forming galaxies are widely regarded as the primary drivers…
With its sensitivity in the rest-frame optical, the James Webb Space Telescope (JWST) has uncovered active galactic nuclei (AGN), comprising both intrinsically faint and heavily reddened sources, well into the first billion years of the…
Active galactic nuclei (AGNs) in the high-redshift Universe are thought to reside in overdense environments. However, recent works provide controversial results partly due to the use of different techniques and possible suppression of…
We discuss the possible origin of the double-peaked profiles recently observed in Lyman-Alpha Emitters (LAEs) at the epoch of reionization ($z \gtrsim 6.5$) from obscured active galactic nuclei (AGN). Combining the extent of the…
Recent observations suggest that hydrogen reionization ends late ($z \simeq 6$) and proceeds quickly. We present here a new model of the meta-galactic UV/X-ray background (UVB) that is consistent with this. It adopts the most recent…
Understanding the sources responsible for reionizing the Universe is a key goal of observational cosmology. A discrepancy has existed between the metagalactic hydrogen ionization rate, Gamma_HI, predicted by early hydrodynamical simulations…
We have evaluated the contribution of the AGN population to the ionization history of the Universe based on a semi-analytic model of galaxy formation and evolution in the CDM cosmological scenario. The model connects the growth of black…
Recent deep surveys have unravelled a population of faint active galactic nuclei (AGN) in the high redshift Universe, leading to various discussions on their nature and their role during the Epoch of Reionization. We use cosmological…
We present here predictions for the spatial distribution of 21 cm brightness temperature fluctuations from high-dynamic-range simulations for AGN-dominated reionization histories that have been tested against available Lyman-alpha and CMB…
In the light of the recent Planck downward revision of the electron scattering optical depth, and of the discovery of a faint AGN population at $z > 4$, we reassess the actual contribution of quasars to cosmic reionization. To this aim, we…
In these proceedings I briefly: (1) review the impact (or "feedback") that active galactic nuclei (AGN) are predicted to have on their host galaxies and larger scale environment, (2) review the observational evidence for or against these…
Lyman Alpha Emitters (LAEs) are usually thought to be powered by star formation. It has been recently reported that a fraction of LAEs at redshift z~3-4 hosts an Active Galactic Nuclei (AGN). If an AGN is present it could be obscured and…
Cosmic reionization put an end to the dark ages that came after the recombination era. Observations seem to favor the scenario where massive stars generating photons in low-mass galaxies were responsible for the bulk of reionization. Even…
We investigate the fraction of z ~ 0.3 Lyman alpha emitting galaxies (LAEs) which host active galactic nucleus activity, which is typically from 1 - 5% at 2 < z < 6. Using optical spectroscopy of 23 LAEs at 0.2 < z < 0.45 selected with…
We reinvestigate a claimed sample of 22 X-ray detected active galactic nuclei (AGN) at redshifts z > 4, which has reignited the debate as to whether young galaxies or AGN reionized the Universe. These sources lie within the GOODS-S/CANDELS…
We explore the kinematics of ionized gas via the [O III] $\lambda$5007 emission lines in active galactic nuclei (AGN) selected on the basis of their mid-infrared (IR) emission, and split into obscured and unobscured populations based on…
We study the observed cosmic ionizing background as a constraint on the nature of the sources responsible for the reionization of the Universe. In earlier work, we showed that extrapolations of the Ultra-Violet Luminosity Function (LF) of…