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 5 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 4x10^{-6} and identify 8 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 Lya narrow-band imaging reveals that a total of 4/123 Lya 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 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_{-4.4}^{+9.2} and 2.9_{-1.6}^{+2.9} per cent, respectively, for protocluster AGN with L_{2-10 keV}>4.6x10^{43} 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 present new observational determinations of the evolution of the 2-10keV X-ray luminosity function (XLF) of AGN. We utilise data from a number of surveys including both the 2Ms Chandra Deep Fields and the AEGIS-X 200ks survey, enabling accurate me
asurements of the evolution of the faint end of the XLF. We combine direct, hard X-ray selection and spectroscopic follow-up or photometric redshift estimates at z<1.2 with a rest-frame UV colour pre-selection approach at higher redshifts to avoid biases associated with catastrophic failure of the photometric redshifts. Only robust optical counterparts to X-ray sources are considered using a likelihood ratio matching technique. A Bayesian methodology is developed that considers redshift probability distributions, incorporates selection functions for our high redshift samples, and allows robust comparison of different evolutionary models. We find that the XLF retains the same shape at all redshifts, but undergoes strong luminosity evolution out to z~1, and an overall negative density evolution with increasing redshift, which thus dominates the evolution at earlier times. We do not find evidence that a Luminosity-Dependent Density Evolution, and the associated flattening of the faint-end slope, is required to describe the evolution of the XLF. We find significantly higher space densities of low-luminosity, high-redshift AGN than in prior studies, and a smaller shift in the peak of the number density to lower redshifts with decreasing luminosity. The total luminosity density of AGN peaks at z=1.2+/-0.1, but there is a mild decline to higher redshifts. We find >50% of black hole growth takes place at z>1, with around half in Lx<10^44 erg/s AGN.
We use morphological information of X-ray selected AGN hosts to set limits on the fraction of the accretion density of the Universe at z~1 that is not likely to be associated with major mergers. Deep X-ray observations are combined with high resoluti
on optical data from the Hubble Space Telescope in the AEGIS, GOODS North and GOODS South fields to explore the morphological breakdown of X-ray sources in the redshift interval 0.5<z<1.3. The sample is split into disks, early-type bulge dominated galaxies, peculiar systems and point-sources in which the nuclear source outshines the host galaxy. The X-ray luminosity function and luminosity density of AGN at z~1 are then calculated as a function of morphological type. We find that disk-dominated hosts contribute 30pm9 per cent to the total AGN space density and 23pm6 per cent to the luminosity density at z~1. We argue that AGN in disk galaxies are most likely fueled not by major merger events but by minor interactions or internal instabilities. We find evidence that these mechanisms may be more efficient in producing luminous AGN (L_X>1e44 erg/s) compared to predictions for the stochastic fueling of massive black holes in disk galaxies.
We present the AEGIS-X survey, a series of deep Chandra ACIS-I observations of the Extended Groth Strip. The survey comprises pointings at 8 separate positions, each with nominal exposure 200ks, covering a total area of approximately 0.67 deg2 in a s
trip of length 2 degrees. We describe in detail an updated version of our data reduction and point source detection algorithms used to analyze these data. A total of 1325 band-merged sources have been found to a Poisson probability limit of 4e-6, with limiting fluxes of 5.3e-17 erg/cm2/s in the soft (0.5-2 keV) band and 3.8e-16 erg/cm2/s in the hard (2-10 keV) band. We present simulations verifying the validity of our source detection procedure and showing a very small, <1.5%, contamination rate from spurious sources. Optical/NIR counterparts have been identified from the DEEP2, CFHTLS, and Spitzer/IRAC surveys of the same region. Using a likelihood ratio method, we find optical counterparts for 76% of our sources, complete to R(AB)=24.1, and, of the 66% of the sources that have IRAC coverage, 94% have a counterpart to a limit of 0.9 microJy at 3.6 microns (m(AB)=23.8). After accounting for (small) positional offsets in the 8 Chandra fields, the astrometric accuracy of the Chandra positions is found to be 0.8 arcsec RMS, however this number depends both on the off-axis angle and the number of detected counts for a given source. All the data products described in this paper are made available via a public website.
