The largest X-ray-selected sample of $\boldsymbol {z>3}$ AGNs: C-COSMOS and ChaMP

Abstract

We present results from an analysis of the largest high-redshift (z > 3) X-ray-selected active galactic nucleus (AGN) sample to date, combining the Chandra C-COSMOS and ChaMP surveys and doubling the previous samples. The sample comprises 209 X-ray-detected AGN, over a wide range of rest frame 2-10 keV luminosities log L X = 43.3 − 46.0 erg s −1 . X-ray hardness rates show that ∼39% of the sources are highly obscured, N H > 10 22 cm −2 , in agreement with the ∼37% of type-2 AGN found in our sample based on their optical classification. For ∼26% of objects have mismatched optical and X-ray classifications. Using the 1/V max method, we confirm that the comoving space density of all luminosity ranges of AGNs decreases with redshift above z > 3 and up to z ∼ 7. With a significant sample of AGN (N = 27) at z > 4, it is found that both source number counts in the 0.5 -2 keV band and comoving space density are consistent with the expectation of a luminosity dependent density evolution (LDDE) model at all redshifts, while they exclude the luminosity and density evolution (LADE) model. The measured comoving space density of type-1 and type-2 AGN shows a constant ratio between the two types at z > 3. Our results for both AGN types at these redshifts are consistent with the expectations of LDDE model.

High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-L* population

“…20 is consistent with previous results by, e.g., Hiroi et al (2012), Kalfountzou et al (2014), Vito et al (2014), andMarchesi et al (2016) (i.e., Φ ∝ (1 + z) p with p ∼ −6, see Tab. 3).…”

“…Vignali et al 2002;Fiore et al 2012;Vito et al 2013;Giallongo et al 2015;Weigel et al 2015;Cappelluti et al 2016) surveys performed with Chandra and XMM -Newton, or using combinations of different surveys (e.g. Kalfountzou et al 2014;Vito et al 2014;Georgakakis et al 2015). Common findings among such works are 1) a decline of the space density of luminous (logLX 44) AGN proportional to (1 + z) d with d ∼ −6 (similar to the exponential decline of the space density of optically selected quasars, e.g., McGreer et al 2013), and 2) a larger fraction of obscured AGN than that usually derived at lower redshifts, particularly at moderate-to-high luminosities (e.g.…”

THE CHANDRA COSMOS-LEGACY SURVEY: THE z > 3 SAMPLE

“…Vito et al (2013), N AGN =34) were able to reach L 2-10 keV ;10 43 erg s −1 using the 4 Ms Chandra Deep Field South (CDF-S, Xue et al 2011) catalog; the same group (Vito et al 2014) studied the 2-10 luminosity function in the redshift range z= [3][4][5] by combining deep and shallow surveys (N AGN = 141). Kalfountzou et al (2014) combined the C-COSMOS sample with the sample from the wide and shallow ChaMP survey (Kim et al 2007;Green et al 2009;Trichas et al 2012) to obtain a sample of N AGN =211 at z>3 and N AGN =27 at z>4, down to a luminosity of L 2-10 keV =10…”

Observational evidence that positive and negative AGN feedback depends on galaxy mass and jet power

“…There are a number of pieces of evidence that support a global evolutionary connection between the star formation and AGN activity, for example, 1) the differential redshift evolution of the AGN luminosity function, or "AGN downsizing" is also found for the star-forming galaxy population (e.g. Hasinger et al 2005;Hopkins & Hernquist 2006;Aird et al 2010;Kalfountzou et al 2014a), 2) the redshift distribution of strongly star-forming galaxies follows that of powerful AGN (e.g. Willott et al 2001;Chapman et al 2005; Wardlow et al…”