F. La Franca et al. 2005 ApJ 635 864 doi:10.1086/497586
The HELLAS2XMM Survey. VII. The Hard X-Ray Luminosity Function of AGNs up to z = 4: More Absorbed AGNs at Low Luminosities and High Redshifts
FREEF. La Franca1, F. Fiore2, A. Comastri3, G. C. Perola1, N. Sacchi1, M. Brusa4, F. Cocchia2, C. Feruglio2, G. Matt1, C. Vignali5, N. Carangelo6, P. Ciliegi3, A. Lamastra1, R. Maiolino7, M. Mignoli3, S. Molendi8 and S. Puccetti2
Show affiliationsWe have determined the cosmological evolution of the density of active galactic nuclei (AGNs) and of their NH distribution as a function of the unabsorbed 2-10 keV luminosity up to redshift 4. We used the HELLAS2XMM sample combined with other published catalogs, yielding a total of 508 AGNs. Our best fit is obtained with a luminosity-dependent density evolution (LDDE) model where low-luminosity (LX ~ 1043 ergs s-1) AGNs peak at z ~ 0.7, while high-luminosity AGNs (LX > 1045 ergs s-1) peak at z ~ 2.0. A pure luminosity evolution model (PLE) can instead be rejected. There is evidence that the fraction of absorbed (NH > 1022 cm-2) AGNs decreases with the intrinsic X-ray luminosity and increases with the redshift. Our best-fit solution provides a good fit to the observed counts, the cosmic X-ray background, and to the observed fraction of absorbed AGNs as a function of the flux in the 10-15 ergs cm-2 s-1 < S2-10 < 10-10 ergs cm-2 s-1 range. We find that the absorbed, high-luminosity (LX > 1044 ergs s-1) AGNs have a density of 267 deg-2 at fluxes S2-10 > 10-15 ergs cm-2 s-1. Using these results, we estimate a density of supermassive black holes in the local universe of ρBH = 3.2 h
× 105 M
Mpc-3, which is consistent with the recent measurements of the black hole mass function in the local galaxies.
- Subject headings
diffuse radiation; galaxies: active; galaxies: evolution; quasars: general; surveys; X-rays: diffuse background
- Dates
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Issue 2 (2005 December 20)
Received 2005 May 16, accepted for publication 2005 August 15
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The HELLAS2XMM Survey. VII. The Hard X-Ray Luminosity Function of AGNs up to z = 4: More Absorbed AGNs at Low Luminosities and High Redshifts
F. La Franca et al. 2005 ApJ 635 864
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