We present the results of spectroscopic, narrow‐band and X‐ray observations of a z= 2.30 protocluster in the field of the QSO HS 1700+643. Using a sample of BX/MD galaxies, which are selected to be at z∼ 2.2–2.7 by their rest‐frame ultraviolet colours, we find that there are five protocluster AGN which have been identified by characteristic emission‐lines in their optical/near‐IR spectra; this represents an enhancement over the field significant at >98.5 per cent confidence. Using a ∼200‐ks Chandra/ACIS‐I observation of this field we detect a total of 161 X‐ray point sources to a Poissonian false‐probability limit of 4 × 10−6 and identify eight of these with BX/MD galaxies. Two of these are spectroscopically confirmed protocluster members and are also classified as emission‐line AGN. When compared to a similarly selected field sample, the analysis indicates this is also evidence for an enhancement of X‐ray selected BX/MD AGN over the field, significant at >99 per cent confidence. Deep Lyα narrow‐band imaging reveals that a total of 4/123 Lyα emitters (LAEs) are found to be associated with X‐ray sources, with two of these confirmed protocluster members and one highly likely member. We do not find a significant enhancement of AGN activity in this LAE sample over that of the field (result is significant at only 87 per cent confidence). The X‐ray emitting AGN fractions for the BX/MD and LAE samples are found to be 6.9+9.2−4.4 and 2.9+2.9−1.6 per cent, respectively, for protocluster AGN with L2‐10 keV≥ 4.6 × 1043 erg s−1 at z= 2.30. These findings are similar to results from the z= 3.09 protocluster in the SSA 22 field found by Lehmer et al. (2009), in that both suggest AGN activity is favoured in dense environments at z > 2.

We explore the nature of Infrared Excess sources (IRX), which are proposed as candidates for luminous [LX(2–10  keV) > 1043  erg   s−1] Compton thick (NH > 2 × 1024  cm−2) QSOs at z≈ 2. Lower redshift, z≈ 1, analogues of the distant IRX population are identified by first redshifting to z= 2 the spectral energy distributions (SEDs) of all sources with secure spectroscopic redshifts in the AEGIS (6488) and the GOODS‐North (1784) surveys and then selecting those that qualify as IRX sources at that redshift. A total of 19 galaxies are selected. The mean redshift of the sample is z≈ 1. We do not find strong evidence for Compton thick QSOs in the sample. For nine sources with X‐ray counterparts, the X‐ray spectra are consistent with Compton thin active galactic nucleus (AGN). Only three of them show tentative evidence for Compton thick obscuration. The SEDs of the X‐ray undetected population are consistent with starburst activity. There is no evidence for a hot dust component at the mid‐infrared associated with AGN heated dust. If the X‐ray undetected sources host AGN, an upper limit of LX(2–10  keV) = 1043  erg   s−1 is estimated for their intrinsic luminosity. We propose that a large fraction of the z≈ 2 IRX population is not Compton thick quasi‐stellar objects (QSOs) but low‐luminosity [LX(2–10  keV) < 1043  erg   s−1], possibly Compton thin, AGN or dusty starbursts. It is shown that the decomposition of the AGN and starburst contribution to the mid‐IR is essential for interpreting the nature of this population, as star formation may dominate this wavelength regime.

Context. The emission line most often observed in the X-ray spectra of active galactic nuclei (AGN) is Fe K α . It is known that it can be broadened and deformed by relativistic effects if emitted close enough to the central super massive black hole (SMBH). Recent statistical studies of the X-ray spectra of AGN samples have found that a narrow Fe line is ubiquitous, while whether the broad features are as common it is still uncertain. Aims. We present here the results of an investigation on the characteristics of the Fe line in the average X-ray spectra of AGN in deep Chandra fields. Methods. The average spectrum of the AGN was computed using Chandra spectra with more than 200 net counts from the AEGIS, Chandra deep field north (CDFN) and Chandra deep field south (CDFS) surveys. The sample spans a broader range of X-ray luminosities than other samples studied with stacking methods up to z ∼ 3.5. We analyzed the average spectra of this sample using our own averaging method, checking the results against extensive simulations. Subsamples defined in terms of column density of the local absorber, redshift, and luminosity were also investigated. Results. We found a very significant Fe line with a narrow profile in all our samples and in almost all the subsamples that we constructed. The equivalent width of the narrow line estimated in the average spectrum of the full sample is 74 eV. In the subsample of AGN with L < 1.43 × 10 44 erg s −1 and z < 0.76, the equivalent width is 108 eV.

Abstract. We present results from a survey of the properties of the central black holes in nearby AGN. This shows that AGN radiating near Eddington are on average less massive now than at z ∼ 1. Keywords. galaxies: active; galaxies: nuclei; accretion, accretion disksWe observed the Ca ii triplet lines near 8550Å in a representative sample of ∼ 150 AGN with z < 0.017. These data were used to derive stellar velocity dispersions (e.g., Nelson & Whittle 1995) and hence black hole masses (Tremaine et al. 2002). We derived accretion rates for 107 of these with measured 25 μm fluxes, using mid-infrared luminosity as a proxy for the luminosity of the AGN (cf. luminosity. Only those objects with MBH < 10 6 . 5 M are near or above Eddington.

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