University of Leicester
Browse

Observational constraints on the specific accretion-rate distribution of X-ray-selected AGNs

Download (3.21 MB)
journal contribution
posted on 2018-08-15, 09:06 authored by A. Georgakakis, J. Aird, A. Schulze, T. Dwelly, M. Salvato, K. Nandra, A. Merloni, D. P. Schneider
This paper estimates the specific accretion-rate distribution of AGNs using a sample of 4821 X-ray sources from both deep and shallow surveys. The specific accretion-rate distribution is used as a proxy of the Eddington ratio and is defined as the probability of a galaxy with a given stellar mass and redshift hosting an active nucleus with a certain specific accretion rate. We find that the probability of a galaxy hosting an AGN increases with decreasing specific accretion rate. There is evidence that this trend reverses at low specific accretion rates, λ ≲ 10^−4 –10^−3 (Eddington units). There is a break close to the Eddington limit, above which the probability of an accretion event decreases steeply. The specific accretion-rate distribution evolves such that the fraction of AGNs among galaxies drops towards lower redshifts. This decrease in the AGN duty cycle is responsible for the strong evolution of the accretion density of the Universe from redshift z ≈ 1–1.5 to the present day. Our analysis also suggests that this evolution is accompanied by a decoupling of accretion events on to black holes from the formation of stars in galaxies. There is also evidence that at earlier times the relative probability of high versus low specific accretion-rate events among galaxies increases. We argue that this differential redshift evolution of the AGN duty cycle with respect to λ produces the AGN downsizing trend, whereby luminous sources peak at earlier epochs compared to less luminous ones. Finally, we also find a stellar mass dependence of the specific accretion-rate distribution, with more massive galaxies avoiding high specific accretion-rate events.

Funding

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’. JA acknowledges support from ERC Advanced Grant FEEDBACK 340442. AS acknowledges support by JSPS KAKENHI Grant Number 26800098. Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science and the Participating Institutions. SDSS acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is www.sdss.org. SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU)/University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatory of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional/MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autonoma de Mexico, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University and Yale University.

History

Citation

Monthly Notices of the Royal Astronomical Society, 2017, 471 (2), pp. 1976-2001

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Version

  • VoR (Version of Record)

Published in

Monthly Notices of the Royal Astronomical Society

Publisher

Oxford University Press (OUP), Royal Astronomical Society

issn

0035-8711

eissn

1365-2966

Acceptance date

2017-06-22

Copyright date

2017

Available date

2018-08-15

Publisher version

https://academic.oup.com/mnras/article/471/2/1976/3892359

Language

en

Usage metrics

    University of Leicester Publications

    Categories

    No categories selected

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC