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On the radiative efficiencies, Eddington ratios, and duty cycles of luminous high-redshift quasars

On the radiative efficiencies, Eddington ratios, and duty cycles of luminous high-redshift quasars
On the radiative efficiencies, Eddington ratios, and duty cycles of luminous high-redshift quasars
We investigate the characteristic radiative efficiency epsilon, Eddington ratio ?, and duty cycle P 0 of high-redshift active galactic nuclei (AGNs), drawing on measurements of the AGN luminosity function at z = 3-6 and, especially, on recent measurements of quasar clustering at z = 3-4.5 from the Sloan Digital Sky Survey. The free parameters of our models are epsilon, ?, and the normalization, scatter, and redshift evolution of the relation between black hole (BH) mass M BH and halo virial velocity V vir. We compute the luminosity function from the implied growth of the BH mass function and the quasar correlation length from the bias of the host halos. We test our adopted formulae for the halo mass function and halo bias against measurements from the large N-body simulation developed by the MICE collaboration. The strong clustering of AGNs observed at z = 3 and, especially, at z = 4 implies that massive BHs reside in rare, massive dark matter halos. Reproducing the observed luminosity function then requires high efficiency epsilon and/or low Eddington ratio ?, with a lower limit (based on 2? agreement with the measured z = 4 correlation length) epsilon gsim 0.7?/(1 + 0.7?), implying epsilon gsim 0.17 for ?>0.25. Successful models predict high duty cycles, P 0 ~ 0.2, 0.5, and 0.9 at z = 3.1, 4.5, and 6, respectively, and they require that the fraction of halo baryons locked in the central BH is much larger than the locally observed value. The rapid drop in the abundance of the massive and rare host halos at z > 7 implies a proportionally rapid decline in the number density of luminous quasars, much stronger than simple extrapolations of the z = 3-6 luminosity function would predict. For example, our most successful model predicts that the highest redshift quasar in the sky with true bolometric luminosity L > 1047.5 erg s–1 should be at z ~ 7.5, and that all quasars with higher apparent luminosities would have to be magnified by lensing
cosmology: theory, galaxies: evolution, galaxies: high-redshift, quasars: general
0004-637X
231-250
Shankar, Francesco
b10c91e4-85cd-4394-a18a-d4f049fd9cdb
Crocce, Martin
65f58884-1a85-41cd-9ef4-93f9fa62578a
Miralda-Escude', Jordi
e0d5ec8c-a2ba-4d29-926d-85ccfe825549
Fosalba, Pablo
7309d371-b57b-4fb5-99f2-1dd419e46285
Weinberg, David H.
40dbbb02-c823-48be-9de0-57567338db5b
Shankar, Francesco
b10c91e4-85cd-4394-a18a-d4f049fd9cdb
Crocce, Martin
65f58884-1a85-41cd-9ef4-93f9fa62578a
Miralda-Escude', Jordi
e0d5ec8c-a2ba-4d29-926d-85ccfe825549
Fosalba, Pablo
7309d371-b57b-4fb5-99f2-1dd419e46285
Weinberg, David H.
40dbbb02-c823-48be-9de0-57567338db5b

Shankar, Francesco, Crocce, Martin, Miralda-Escude', Jordi, Fosalba, Pablo and Weinberg, David H. (2010) On the radiative efficiencies, Eddington ratios, and duty cycles of luminous high-redshift quasars. The Astrophysical Journal, 718 (1), 231-250. (doi:10.1088/0004-637X/718/1/231).

Record type: Article

Abstract

We investigate the characteristic radiative efficiency epsilon, Eddington ratio ?, and duty cycle P 0 of high-redshift active galactic nuclei (AGNs), drawing on measurements of the AGN luminosity function at z = 3-6 and, especially, on recent measurements of quasar clustering at z = 3-4.5 from the Sloan Digital Sky Survey. The free parameters of our models are epsilon, ?, and the normalization, scatter, and redshift evolution of the relation between black hole (BH) mass M BH and halo virial velocity V vir. We compute the luminosity function from the implied growth of the BH mass function and the quasar correlation length from the bias of the host halos. We test our adopted formulae for the halo mass function and halo bias against measurements from the large N-body simulation developed by the MICE collaboration. The strong clustering of AGNs observed at z = 3 and, especially, at z = 4 implies that massive BHs reside in rare, massive dark matter halos. Reproducing the observed luminosity function then requires high efficiency epsilon and/or low Eddington ratio ?, with a lower limit (based on 2? agreement with the measured z = 4 correlation length) epsilon gsim 0.7?/(1 + 0.7?), implying epsilon gsim 0.17 for ?>0.25. Successful models predict high duty cycles, P 0 ~ 0.2, 0.5, and 0.9 at z = 3.1, 4.5, and 6, respectively, and they require that the fraction of halo baryons locked in the central BH is much larger than the locally observed value. The rapid drop in the abundance of the massive and rare host halos at z > 7 implies a proportionally rapid decline in the number density of luminous quasars, much stronger than simple extrapolations of the z = 3-6 luminosity function would predict. For example, our most successful model predicts that the highest redshift quasar in the sky with true bolometric luminosity L > 1047.5 erg s–1 should be at z ~ 7.5, and that all quasars with higher apparent luminosities would have to be magnified by lensing

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Published date: 20 July 2010
Keywords: cosmology: theory, galaxies: evolution, galaxies: high-redshift, quasars: general
Organisations: Physics & Astronomy

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Local EPrints ID: 357033
URI: http://eprints.soton.ac.uk/id/eprint/357033
ISSN: 0004-637X
PURE UUID: 21a4827b-f053-4821-aa2d-40eb5a0fe226

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Date deposited: 19 Sep 2013 10:14
Last modified: 25 Nov 2021 17:07

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Contributors

Author: Martin Crocce
Author: Jordi Miralda-Escude'
Author: Pablo Fosalba
Author: David H. Weinberg

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