Faint high-redshift AGN in the Chandra deep field south: the evolution of the AGN luminosity function and black hole demography

摘要

Context. We present detection and analysis of faint X-ray sources in the Chandra deep field south (CDFS) using the 4?Ms Chandra observation. Aims. We place constraints on active galactic nuclei (AGN) luminosity functions at z?=?3–7, its cosmological evolution, and high-redshift black hole and AGN demography. Methods. We use a new detection algorithm, using the entire three-dimensional data-cube (position and energy), and searching for X-ray counts at the position of high-z galaxies in the GOODS-South survey. Results. This optimized technique results in the identification of 54?AGN at z?>?3, 29 of which are new detections. Applying stringent completeness criteria, we derive AGN luminosity functions in the redshift bins 3–4, 4–5, and ?>?5.8 and for 42.75???3 (18-10+17 %). Their optical counterparts do not show any reddening and we thus conclude that the size of the X-ray absorber is likely smaller than the dust sublimation radius. We finally report the discovery of a highly star-forming galaxy at z?=?3.47, arguing that its X-ray luminosity is likely dominated by stellar sources. If confirmed, this would be one of the farthest objects in which stellar sources have been detected in X-rays.