We have determined the cosmological evolution of the density of active galactic nuclei (AGNs) and of their N-H 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 (L-X similar to 10(43) ergs s(-1)) AGNs peak at z similar to 0.7, while high-luminosity AGNs (L-X > 10(45) ergs s(-1)) peak at z similar to 2.0. A pure luminosity evolution model (PLE) can instead be rejected. There is evidence that the fraction of absorbed (N-H > 10(22) 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 (L-X > 10(44) 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 rho(BH) = 3.2 h(70)(2) x 10(5) M-circle dot Mpc(-3), which is consistent with the recent measurements of the black hole mass function in the local galaxies.

LA FRANCA, F., Fiore, F., Comastri, A., Perola, G.c., Sacchi, N., Brusa, M., et al. (2005). 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. THE ASTROPHYSICAL JOURNAL, 635(2), 864-879 [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

LA FRANCA, Fabio;MATT, Giorgio;
2005-01-01

Abstract

We have determined the cosmological evolution of the density of active galactic nuclei (AGNs) and of their N-H 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 (L-X similar to 10(43) ergs s(-1)) AGNs peak at z similar to 0.7, while high-luminosity AGNs (L-X > 10(45) ergs s(-1)) peak at z similar to 2.0. A pure luminosity evolution model (PLE) can instead be rejected. There is evidence that the fraction of absorbed (N-H > 10(22) 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 (L-X > 10(44) 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 rho(BH) = 3.2 h(70)(2) x 10(5) M-circle dot Mpc(-3), which is consistent with the recent measurements of the black hole mass function in the local galaxies.
LA FRANCA, F., Fiore, F., Comastri, A., Perola, G.c., Sacchi, N., Brusa, M., et al. (2005). 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. THE ASTROPHYSICAL JOURNAL, 635(2), 864-879 [10.1086/497586].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11590/120570
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