Faint high-redshift AGN in the Chandra deep field south: the evolution of the AGN luminosity function and black hole demography ⋆
1 Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
2 ASI Science Data Center, via Galileo Galilei, 00044 Frascati, Italy
3 Max-Planck-Institut fur Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
5 Università di Roma La Sapienza, Piazzale Aldo Moro 5, 00185 Roma, Italy
6 Institut de RadioAstronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406 Saint Martin d’ Hères, France
7 Astronomy Department, Ohio State University, Columbus, OH - 43210, USA
8 Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
9 CEA/DSM-CNRS, Université Paris Diderot, DAPNIA/SAp, Orme des Merisiers, 91191 Gif-sur-Yvette, France
Received: 28 June 2011
Accepted: 11 September 2011
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 < log L(2–10 keV) < 44.5. We combine this data with the luminous AGN luminosity functions from optical surveys and find that the evolution of the high-z, wide luminosity range luminosity function can be modeled by pure luminosity evolution with L∗ decreasing from 6.6 × 1044 erg/s at z = 3 to L∗ = 2 × 1044 erg/s at z = 6. We compare the high-z luminosity function with the predictions of theoretical models using galaxy interactions as AGN triggering mechanism. We find that these models are broadly able to reproduce the high-z AGN luminosity functions. Closer agreement is found when we assume a minimum dark matter halo mass for black hole formation and growth. We compare our AGN luminosity functions with galaxy mass functions to derive the high-z AGN duty cycle, using observed Eddington ratio distributions to derive black hole masses. We find that the duty cycle increases with galaxy stellar mass and redshift by a factor of 10–30 from z = 0.25 to z = 4–5. We also report the detection of a large fraction of highly obscured, Compton thick AGN at z > 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.
Key words: accretion, accretion disks / black hole physics / galaxies: active / X-rays: galaxies
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2012