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

Abstract

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 highredshift 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 × 10 44 erg/s at z = 3 to L * = 2 × 10 44 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 +17 −10 %). 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.

High-redshift active galactic nuclei and H I reionisation: limits from the unresolved X-ray background

“…Indications along such line have been reported by several groups (Glikman et al 2011;Civano et al 2011;Fiore et al 2012), although it is fair to say that results seem not univocal (see, e.g., Masters et al 2012). Very recently, Giallongo et al (2015) found 22 AGN candidates at z 4 in the Candel/GOOD-S/Chandra Deep Field South field, which is suggestive of a prominent contribution of AGNs to the ionising background in the range 4 z 6.5.…”

Nuclear activity versus star formation: emission-line diagnostics at ultraviolet and optical wavelengths

“…Cowie et al 2009;Willott et al 2010;Fontanot et al 2012), although quasars, mini-quasars and a faint AGN population could also play a significant role (e.g. Volonteri & Gnedin 2009;Fiore et al 2012;Haardt & Salvaterra 2015;Hao et al 2015).…”

Physical properties of AGN host galaxies as a probe of supermassive black hole feeding mechanisms

“…For the IT scenario, the black solid line represents the host stellar mass function predicted by the model; for the DI scenario, the red solid line represents the predictions for the fiducial case (α = 10), while the red dashed line represents the case with the normalization of the accretion rate decreased (α = 2). The blue dotted line represents the host stellar mass function estimate from Fiore et al (2012) as computed by the authors at redshift 0.75, 1.25, 2, and 3.5. The shaded region represents the observational data from Bongiorno et al (in prep.…”

“…We also compared our results with the empirical estimates of the host stellar mass function from Fiore et al (2012). The authors first converted the X-ray AGN luminosity functions (taken from La Franca et al 2005 for z < ∼ 2 and from their work for z > 3) into BH mass functions using Monte Carlo realizations and assuming a given Eddington ratio distribution.…”

“…Assuming a broader distribution in computing the mass incompleteness -at least for the most massive, passive hostswould result in higher abundance of massive hosts, which might reduce the mismatch with IT predictions in the lowest redshift bin. The Eddington ratio distribution also critically affects the host mass function estimates from Fiore et al (2012); the authors note that the normalization at M * = 10 11 M changes by a factor of 15−30% and ∼100% for a distribution peak and width differing by 30% from the assumed normalizations. At high redshift, the uncertainties related to the X-ray AGN luminosity function or possible deviations in the SMBH mass-bulge mass relation can also affect the host mass function calculations, especially at low masses.…”