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The evolution of active galactic nuclei across cosmic time: what is downsizing?

Fanidakis, N. and Baugh, C. M. and Benson, A. J. and Bower, R. G. and Cole, S. and Done, C. and Frenk, C. S. and Hickox, R. C. and Lacey, C. and del P. Lagos, C. (2012) The evolution of active galactic nuclei across cosmic time: what is downsizing? Monthly Notices of the Royal Astronomical Society, 419 (4). pp. 2797-2820. ISSN 0035-8711.

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We use a coupled model of the formation and evolution of galaxies and black holes (BHs) to study the evolution of active galactic nuclei (AGNs) in a cold dark matter universe. The model is embedded in the galaxy formation code galform and predicts the masses, spins and mass accretion histories of BHs in tandem with the formation of their host galaxies. BHs grow by accretion during starbursts, triggered by discs becoming dynamically unstable or by galaxy mergers, and accretion from quasi-hydrostatic hot gas haloes. Using an empirical law for AGN obscuration, our model matches the observed luminosity functions (LFs) of AGNs over a wide range of redshifts. Due to the suppression of cooling in massive haloes by AGN feedback, at low redshift (z≲2), the brightest quasars (L_(bol)≳ 10^(46) erg s^(−1)) are predicted preferentially to inhabit haloes with masses ≃ 10^(12)–10^(13) M_⊙. The model predicts a hierarchical buildup of BH mass, with the typical mass of actively growing BHs increasing with decreasing redshift. Nevertheless, the model displays clear ‘downsizing’ as reflected in the differential evolution of the space density of faint and bright AGNs. This arises naturally from the interplay between the starburst and hot gas halo accretion modes. The faint end of the LF is dominated by massive BHs accreting at low rates via a thick disc, primarily during the hot-halo mode. The bright end is populated by BHs accreting close to or above the Eddington limit during the starburst mode. Obscuration plays a central role in determining the observed abundance of AGNs and, hence, in their implied cosmic evolution.

Item Type:Article
Related URLs:
URLURL TypeDescription
Fanidakis, N.0000-0003-4990-1160
Baugh, C. M.0000-0002-9935-9755
Benson, A. J.0000-0001-5501-6008
Bower, R. G.0000-0002-5215-6010
Done, C.0000-0002-1065-7239
Frenk, C. S.0000-0002-2338-716X
Hickox, R. C.0000-0003-1468-9526
Lacey, C.0000-0001-9016-5332
del P. Lagos, C.0000-0003-3021-8564
Additional Information:© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 September 28. Received 2011 July 13; in original form 2010 November 22. Article first published online: 1 Dec 2011. NF acknowledges receipt of a fellowship funded by the European Commission’s Framework Programme 6, through the Marie Curie Early Stage Training Project MEST-CT-2005-021074. AJB acknowledges the support of the Gordon & Betty Moore Foundation. SC acknowledges the support of a Leverhulme research fellowship. CSF acknowledges a Royal Society Wolfson Research Merit Award. This work was supported in part by an STFC Rolling Grant to the Institute for Computational Cosmology.
Group:Moore Center for Theoretical Cosmology and Physics, TAPIR
Funding AgencyGrant Number
Marie Curie FellowshipMEST-CT-2005-021074
Gordon and Betty Moore FoundationUNSPECIFIED
Leverhulme TrustUNSPECIFIED
Science and Technology Facilities Council (STFC)UNSPECIFIED
Subject Keywords: methods: numerical; galaxies: active; galaxies: nuclei; quasars: general
Issue or Number:4
Record Number:CaltechAUTHORS:20120319-104412300
Persistent URL:
Official Citation:Fanidakis, N., Baugh, C. M., Benson, A. J., Bower, R. G., Cole, S., Done, C., Frenk, C. S., Hickox, R. C., Lacey, C. and del P. Lagos, C. (2012), The evolution of active galactic nuclei across cosmic time: what is downsizing?. Monthly Notices of the Royal Astronomical Society, 419: 2797–2820. doi: 10.1111/j.1365-2966.2011.19931.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:29768
Deposited By: Ruth Sustaita
Deposited On:19 Mar 2012 18:05
Last Modified:11 Dec 2020 20:53

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