OBSCURATION-DEPENDENT EVOLUTION OF ACTIVE GALACTIC NUCLEI

By J. Buchner, A. Georgakakis, K. Nandra, M. Brightman, M. Menzel, Zhu Liu, L. Hsu, Mara Salvato, C. Rangel, J. Aird and 2 more. 2015

161 citations recorded by the source corpus.

We aim to constrain the evolution of active galactic nuclei (AGNs) as a function of obscuration using an X-ray-selected sample of ∼2000 AGNs from a multi-tiered survey including the CDFS, AEGIS-XD, COSMOS, and XMM-XXL fields. The spectra of individual X-ray sources are analyzed using a Bayesian methodology with a physically realistic model to infer the posterior distribution of the hydrogen column density and intrinsic X-ray luminosity. We develop a novel non-parametric method that allows us to robustly infer the distribution of the AGN population in X-ray luminosity, redshift, and obscuring column density, relying only on minimal smoothness assumptions. Our analysis properly incorporates uncertainties from low count spectra, photometric redshift measurements, association incompleteness, and the limited sample size. We find that obscured AGNs with NH > 1022 cm−2 account for of the number density and luminosity density of the accretion supermassive black hole population with LX > 1043 erg s−1, averaged over cosmic time. Compton-thick AGNs account for approximately half the number and luminosity density of the obscured population, and of the total. We also find evidence that the evolution is obscuration dependent, with the strongest evolution around NH ≈ 1023 cm−2. We highlight this by measuring the obscured fraction in Compton-thin AGNs, which increases toward z ∼ 3, where it is 25% higher than the local value. In contrast, the fraction of Compton-thick AGNs is consistent with being constant at ≈35%, independent of redshift and accretion luminosity. We discuss our findings in the context of existing models and conclude that the observed evolution is, to first order, a side effect of anti-hierarchical growth.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/735afbe9a0e1436b43e7fae9ab230d87ceff4b31

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Citations in the corpus

The dust covering factor in active galactic nuclei (2016, background): “The decrease of the covering factor of the torus with increasing luminosity is systematically found in X-ray surveys (e.g. Ueda et al. 2003; Beckmann et al. 2009; Burlon et al. 2011; Ricci et al. 2013; Merloni et al. 2014; Ueda et al. 2014; Buchner et al. 2015).”
The Romulus cosmological simulations: a physical approach to the formation, dynamics and accretion models of SMBHs (2016, background): “This makes them less sensitive to absorption, which can significantly impact optical and X-ray observations across all redshifts (Treister et al. 2010; Lansbury et al. 2015; Buchner et al. 2015; Lacy et al. 2015).”
The bolometric quasar luminosity function at z = 0–7 (2020, methodology): “…and the CTK quasar fraction from this model with observations (Ueda et al. 2003; Burlon et al. 2011; Brightman & Ueda 2012; Merloni et al. 2014; Aird et al. 2015a; Buchner et al. 2015; Ricci et al. 2015; Del Moro et al. 2016; Georgakakis et al. 2017; Masini et al. 2018; Lanzuisi et al. 2018).”
COMPTON-THICK ACCRETION IN THE LOCAL UNIVERSE (2015, background): “…band, and recent deep surveys carried out with Chandra and XMMNewton in the 0.3–10 keV range (e.g., COSMOS, Chandra deep field south) have been able to find a considerable number of CT AGNs at z1 (e.g., Georgantopoulos et al. 2013; Vignali et al. 2014; Buchner et al. 2015; Lanzuisi et al. 2015).”
Active galactic nuclei: what’s in a name? (2017, background): “The symbols indicate the data for AGN from Miyaji et al. (2015) in different X-ray luminosity bins while the curves and shaded regions indicate the models for the evolution of X-ray selected AGN from Aird et al. (2015).”
The cosmic evolution of massive black holes in the Horizon-AGN simulation (2016, methodology): “We also adopt the most recent hard X-ray LF (2–10 keV; Buchner et al. 2015), which includes a correction for obscured (1022 < NH < 1024 cm−2, where NH is the equivalent neutral hydrogen column density) and Compton thick AGN (NH > 1024 cm−2) – but estimating the contribution of the elusive Compton…”
The Illustris simulation: the evolving population of black holes across cosmic time (2014, background): “Finally, it is interesting to note that a recent paper by Buchner et al. (2015) advocates significantly larger uncertainties at the faint-end of the AGN luminosity function which stem from their non-parametric approach.”
Blossoms from black hole seeds: properties and early growth regulated by supernova feedback (2016, methodology): “10), the BH luminosity function of this model is the closest to the bolometric and X-ray luminosity functions derived respectively by Hopkins, Richards & Hernquist (2007), and Buchner et al. (2015) (Fig.”
New Spectral Model for Constraining Torus Covering Factors from Broadband X-Ray Spectra of Active Galactic Nuclei (2018, background): “It has been suggested that the covering factor depends on the Eddington ratio (e.g., Ezhikode et al. 2017, Buchner & Bauer 2017, Ricci et al. 2017b), and that its dependence on luminosity or the Eddington ratio changes with redshift (e.g., Aird et al. 2015, Buchner et al. 2015).”
Supermassive black holes and their feedback effects in the IllustrisTNG simulation (2017, background): “We note however that the exact number of Compton-thick AGN at low luminosities is uncertain (Buchner et al. 2015), thus the observational uncertainties in this regime are substantial.”
THE CHANDRA COSMOS LEGACY SURVEY: OPTICAL/IR IDENTIFICATIONS (2015, background): “…in unobscured and obscured sources on the basis of both the optical spectroscopic classification and X-ray absorption properties; Ueda et al. (2014), who also found that at higher redshifts the decline of the obscured AGN fraction starts at higher luminosities; and lastly Buchner et al. (2015).”