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Investigating evidence for different black hole accretion modes since redshift z ∼ 1



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Georgakakis, A. and Pérez González, Pablo Guillermo and Fanidakis, N. and Salvato, M. and Aird, J. and Messias, H. and Lotz, J. M. and Barro, Guillermo and Hsu, Li-Ting and Nandra, K. and Rosario, D. and Cooper, M. C. and Kocevski, D. d. and Newman, J. A. (2014) Investigating evidence for different black hole accretion modes since redshift z ∼ 1. Monthly notices of the Royal Astronomical Society, 440 (1). pp. 339-352. ISSN 0035-8711


Official URL: http://dx.doi.org/10.1093/mnras/stu236


Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U − V versus V − J colours of X-ray AGN hosts in the redshift intervals 0.1 < z < 0.6 (mean z¯=0.40) and 0.6 < z < 1.2 (mean z¯=0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by their U − V versus V − J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early- and late-type hosts. The position of AGN hosts on the U − V versusV − J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z≈ 0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15–20 per cent, at both z¯=0.40 and 0.85, is taking place in galaxies in the quiescent region of the U − V versus V − J diagram. For the low-redshift sub-sample, 0.1 < z < 0.6, we also find tentative evidence, significant at the 2σ level, that AGN split by their U − V and V − J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift, z > 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≳ 10^− 3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies. We compare these results with the predictions of theGALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z < 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data.

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© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
The authors wish to thank the referee, M. Brusa, for providing constructive comments and suggestions. PGP-G acknowledges support from the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA2012-31277. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). Funding for the DEEP2 Galaxy Redshift Survey has been provided in part by NSF grants AST95-09298, AST-0071048, AST-0071198, AST-0507428 and AST-0507483 as well as NASA LTSA grant NNG04GC89G. Funding for the DEEP3 Galaxy Redshift Survey has been provided by NSF grants AST-0808133, AST-0807630 and AST-0806732. This work benefited from the THALES project 383549 that is jointly funded by the European Union and the Greek Government in the framework of the programme 'Education and lifelong learning'.

Uncontrolled Keywords:Active galactic nuclei; Hubble-space-telescope; Star-forming galaxies; Extended groth strip; Origins deep survey; Digital sky survey; Wide-field survey; X-ray AGN; Host galaxies; Cosmos field
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:38345
Deposited On:30 Jun 2016 14:51
Last Modified:10 Dec 2018 15:05

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