Lifting the Veil on Obscured Accretion: Active Galactic Nuclei Number Counts and Survey Strategies for Imaging Hard X-Ray Missions

Ballantyne, D. R.; Draper, Aden R.; Madsen, K. K.; Rigby, J. Keith; Treister, Ezequiel

doi:10.1088/0004-637x/736/1/56

Cited by 84 publications

(120 citation statements)

References 105 publications

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“…Indeed, the CXB can be reproduced with a wide variety of models that assume different X-ray spectral models for the constituent AGNs, as well as different XLFs, NH distributions, and-perhaps most crucially-Comptonthick fractions (e.g. Draper & Ballantyne 2009;Ballantyne et al 2011;Akylas et al 2012). While fully exploring CXB synthesis models for different spectral models and Compton-thick fractions is beyond the scope of this work, Figure 17 does indicate that our relatively low Compton-thick fraction should not be ruled out.…”

Section: The Nh Distribution the Fraction Of Compton-thick Agns And mentioning

confidence: 99%

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

Aird

Coil

Georgakakis

et al. 2015

Monthly Notices of the Royal Astronomical Society

375

559

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We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed Active Galactic Nuclei (AGNs) out to z ∼ 5. We construct samples containing 2957 sources detected at hard (2-7 keV) X-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break luminosity, normalization and faint-end slope all evolve with redshift. We then incorporate absorption effects, separately modelling the evolution of the XLFs of unabsorbed (20 < log N H < 22) and absorbed (22 < log N H < 24) AGNs, seeking a model that can reconcile both the hard-and soft-band samples. We find that the absorbed AGN XLF has a lower break luminosity, a higher normalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to z ∼ 2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed fraction falling rapidly as luminosity increases. Both XLFs undergo strong luminosity evolution which shifts the transition in the absorbed fraction to higher luminosities at higher redshifts. The evolution in the shape of the total XLF is primarily driven by the changing mix of unabsorbed and absorbed populations.

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Section: The Nh Distribution the Fraction Of Compton-thick Agns And mentioning

confidence: 99%

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

Aird

Coil

Georgakakis

et al. 2015

Monthly Notices of the Royal Astronomical Society

375

559

View full text Add to dashboard Cite

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“…Indeed, given the paucity of CT sources effectively contributing to the CXB missing flux, the most recent population-synthesis models have tried to explain the CXB missing component as mainly a pronounced reflection contribution from less obscured sources with a reduced contribution by CT AGN (Treister et al 2009;Ballantyne et al 2011;Akylas et al 2012).…”

Section: Introductionmentioning

confidence: 99%

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

Zappacosta

Comastri

Civano

et al. 2018

ApJ

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We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S 8 24 keV 7 10 14 =´-( -) erg s cm 1 2 --in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z 0 2.1 = -(median z 0.58 á ñ = ). The spectral analysis is performed over the broad 0.5-24keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at 10 keV > to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (N H ), reflection parameter (R), and 10-40keV luminosity (L X ). Heavily obscured ( N log cm 23AGN constitute ∼25% (15-17 sources) and ∼2-3% (1-2 sources) of the sample, respectively. The observed N H distribution agrees fairly well with predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of N H , accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to N log cm 20 24AGN is poorly constrained, formally in the range 2-56% (90% upper limit of 66%). We derived a fraction ( f abs ) of obscured AGN ( N log cm 22 24as a function of L X in agreement with CXBPSM and previous z 1 < X-ray determinations. Furthermore, f abs at z 0.1 0.5 = -and L log erg s 43.6 44.3agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with L X (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.

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“…The X-ray background is mainly due to the X-ray emission from SMBH, but unlike the luminosity function, which is derived from the observed sources, it incorporates the emission from heavily obscured AGN most of which are too faint to be detected even in the deepest X-ray surveys. A number of models have been developed to reconstruct the spectrum of the X-ray background (Comastri et al 1995;Gilli et al 2007;Treister et al 2009;Ballantyne et al 2011;Akylas et al 2012;Ueda et al 2014). All these models require a substantial number of Compton-thick AGN to reproduce the peak of the spectrum between 20 and 30 keV (Marshall et al 1980a;Gruber et al 1999;Revnivtsev et al 2003;Frontera et al 2007;Ajello et al 2008;Moretti et al 2009;Türler et al 2010).…”

Section: Introductionmentioning

confidence: 99%

Compton-thick AGN in the 70-monthSwift-BAT All-Sky Hard X-ray Survey: A Bayesian approach

Akylas

Georgantopoulos

Ranalli

et al. 2016

A&A

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The 70-month Swift/BAT catalogue provides a sensitive view of the extragalactic X-ray sky at hard energies (>10 keV) containing about 800 active galactic nuclei (AGN). We explore its content in heavily obscured, Compton-thick AGN by combining the BAT (14-195 keV) with the lower energy XRT (0.3-10 keV) data. We apply a Bayesian methodology using Markov chains to estimate the exact probability distribution of the column density for each source. We find 53 possible Compton-thick sources (probability range 3 -100%) translating to a ∼7% fraction of the AGN in our sample. We derive the first parametric luminosity function of Compton-thick AGN. The unabsorbed luminosity function can be represented by a double power law with a break at L ∼ 2 × 10 42 ergs s −1 in the 20-40 keV band. The Compton-thick AGN contribute ∼17% of the total AGN emissivity. We derive an accurate Compton-thick number count distribution taking into account the exact probability of a source being Compton-thick and the flux uncertainties. This number count distribution is critical for the calibration of the X-ray background synthesis models, i.e. for constraining the intrinsic fraction of Compton-thick AGN. We find that the number counts distribution in the 14-195 keV band agrees well with our models which adopt a low intrinsic fraction of Compton-thick AGN (∼ 12%) among the total AGN population and a reflected emission of ∼ 5%. In the extreme case of zero reflection, the number counts can be modelled with a fraction of at most 30% Compton-thick AGN of the total AGN population and no reflection. Moreover, we compare our X-ray background synthesis models with the number counts in the softer 2-10 keV band. This band is more sensitive to the reflected component and thus helps us to break the degeneracy between the fraction of Compton-thick AGN and the reflection emission. The number counts in the 2-10 keV band are well above the models which assume a 30% Compton-thick AGN fraction and zero reflection, while they are in better agreement with models assuming 12% Compton-thick fraction and 5% reflection. The only viable alternative for models invoking a high number of Compton-thick AGN is to assume evolution in their number with redshift. For example, in the zero reflection model the intrinsic fraction of Compton-thick AGN should rise from 30% at redshift z∼ 0 to about 50% at a redshift of z=1.1.

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Lifting the Veil on Obscured Accretion: Active Galactic Nuclei Number Counts and Survey Strategies for Imaging Hard X-Ray Missions

Cited by 84 publications

References 105 publications

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

The evolution of the X-ray luminosity functions of unabsorbed and absorbed AGNs out to z∼ 5

The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

Compton-thick AGN in the 70-monthSwift-BAT All-Sky Hard X-ray Survey: A Bayesian approach

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