ﻻ يوجد ملخص باللغة العربية
We use highly spectroscopically complete deep and wide-area Chandra surveys to determine the cosmic evolution of hard X-ray-selected AGNs. We determine hard X-ray luminosity functions (HXLFs) for all spectral types and for broad-line AGNs (BLAGNs) alone. At z<1.2, both are well described by pure luminosity evolution. Thus, all AGNs drop in luminosity by almost an order of magnitude over this redshift range. We show that this observed drop is due to AGN downsizing. We directly compare our BLAGN HXLFs with the optical QSO LFs and find that the optical QSO LFs do not probe faint enough to see the downturn in the BLAGN HXLFs. We rule out galaxy dilution as a partial explanation for the observation that BLAGNs dominate the number densities at the higher X-ray luminosities, while optically-narrow AGNs (FWHM<2000 km/s) dominate at the lower X-ray luminosities by measuring the nuclear UV/optical properties of the Chandra sources using the HST ACS GOODS-North data. The UV/optical nuclei of the optically-narrow AGNs are much weaker than expected if they were similar to the BLAGNs. We therefore postulate the need for a luminosity dependent unified model. Alternatively, the BLAGNs and the optically-narrow AGNs could be intrinsically different source populations. We cover both interpretations by constructing composite spectral energy distributions--including long-wavelength data from the MIR to the submillimeter--by spectral type and by X-ray luminosity. We use these to infer the bolometric corrections (from hard X-ray luminosities to bolometric luminosities) needed to map the accretion history. We determine the accreted supermassive black hole mass density for all spectral types and for BLAGNs alone using the observed evolution of the hard X-ray energy density production rate and our inferred bolometric corrections.
We present results of near-infrared photometry (J, H, K_S) for a sample of active galactic nuclei (AGNs) obtained from hard X-ray surveys with ASCA. The sample covers the AGNs at z=0.1-1 with L(2-10keV)=10^42-10^46 erg/s with very high completeness.
We present X-ray and optical analysis of 188 AGN identified from 497 hard X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These medium depth X-ray obse
We study properties of the host galaxies of 15 hard X-ray selected type-2 active galactic nuclei (AGNs) at intermediate redshifts (0.05$<z<$0.6) detected in $ASCA$ surveys. The absorption corrected hard X-ray luminosities $L_{rm 2-10 keV}$ range from
Merger simulations predict that tidally induced gas inflows can trigger kpc-scale dual active galactic nuclei (dAGN) in heavily obscured environments. Previously with the Very Large Array, we have confirmed four dAGN with redshifts between $0.04 < z
Hard X-ray surveys are an important tool for the study of active galactic nuclei (AGN): they provide almost an unbiased view of absorption in the extragalactic population, allow the study of spectral features such as reflection and high energy cut-of