Astrophys. J., 570, 100-113 (2002/May-1)
The BeppoSAX high-energy large-area survey. V. The nature of the hard X-ray source population and its evolution.
LA FRANCA F., FIORE F., VIGNALI C., ANTONELLI A., COMASTRI A., GIOMMI P., MATT G., MOLENDI S., PEROLA G.C. and POMPILIO F.
Abstract (from CDS):
We present optical spectroscopic identifications of hard X-ray (5-10 keV) selected sources belonging to the High-Energy Large-Area Survey sample obtained with BeppoSAX down to a 5-10 keV flux limit of f5–10keV∼3x10–14 ergs. cm–2.s–1. The sample consists of 118 sources. There are 25 sources that have been identified through correlations with catalogs of known sources. A spectroscopic identification for 49 more has been searched for with the telescope. The results of 13 fields were empty down to R=21. There were 37 sources identified as type 1 active galactic nuclei (AGNs) and nine as type 2 AGNs. The remaining sources are five narrow emission-line galaxies, six clusters, two BL Lac objects, one radio galaxy, and one star. Combining these objects with other hard X-ray selected AGNs from ASCA and HEAO 1, we find that the local luminosity function of type 1 AGNs (AGN 1s) in the 2-10 keV band is fairly well represented by a double power law function. There is evidence for significant cosmological evolution according to a pure luminosity evolution (PLE) model [LX(z)∝(1+z)k], with k=2.12 and 2.22 (σk≃0.14) in a (Ωm,Ωλ)=(1.0,0.0) and a (Ωm,Ωλ)=(0.3,0.7) cosmology, respectively. The data show an excess of faint high-redshift type AGN 1s, which is well modeled by a luminosity-dependent density evolution (LDDE), similar to what is observed in soft X-rays. However, in both cosmologies, the statistics are not significant enough to distinguish between the PLE and LDDE models. The fitted models imply a contribution of AGN 1s to the 2-10 keV X-ray background from 35% up to 60%.
Cosmology: Observations - Galaxies: Active - Galaxies: Distances and Redshifts - Galaxies: Evolution - Galaxies: Quasars: General
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<Available at CDS (J/ApJ/570/100): table3.dat table4.dat table5.dat>
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