The NuSTAR Extragalactic Surveys: Source Catalog and the Compton-thick Fraction in the UDS Field

Masini, Alberto; Civano, F.; Comastri, A.; Fornasini, Francesca M.; Ballantyne, D. R.; Lansbury, G. B.; Treister, Ezequiel; Alexander, D. M.; Boorman, Peter; Brandt, W. N.; Farrah, D.; Gandhi, P.; Harrison, Fiona A.; Hickox, Ryan C.; Kocevski, Dale D.; Lanz, Lauranne; Marchesi, S.; Puccetti, S.; Ricci, Cláudio; Saez, C.; Stern, Daniel; Zappacosta, L.

doi:10.3847/1538-4365/aaa83d

Cited by 37 publications

(48 citation statements)

References 67 publications

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“…In contrast, the model with the enhanced Compton-thick fraction appears to more accurately describe the Compton-thick counts at these fainter fluxes. This latter model has a Compton-thick fraction of 0.14 at a 8-24 keV flux of 2.7 × 10 −14 erg cm −2 s −1 , very similar to what is measured from NuSTAR observations (Masini et al 2018). The picture that emerges from these experiments is one where both the reflection fraction and possibly the Compton-thick fraction increase with z.…”

Section: The Impact Of the Compton-thick Fractionsupporting

confidence: 80%

The evolving X-ray spectrum of active galactic nuclei: evidence for an increasing reflection fraction with redshift

Avirett-Mackenzie

Ballantyne

2019

Monthly Notices of the Royal Astronomical Society

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The cosmic X-ray background (XRB) spectrum and active galaxy number counts encode essential information about the spectral evolution of active galactic nuclei (AGNs) and have been successfully modeled by XRB synthesis models for many years. Recent measurements of the 8-24 keV AGN number counts by NuSTAR and Swift-BAT are unable to be simultaneously described by existing XRB synthesis models, indicating a fundamental breakdown in our understanding of AGN evolution. Here we show that the 8-24 keV AGN number counts can be successfully modeled with an XRB synthesis model in which the reflection strength (R) in the spectral model increases with redshift. We show that an increase in reflection strength with redshift is a natural outcome of (1) connecting R to the incidence of high column density gas around AGNs, and (2) the growth in the AGN obscured fraction to higher redshifts. In addition to the redshift evolution of R, we also find tentative evidence that an increasing Compton-thick fraction with z is necessary to describe the 8-24 keV AGN number counts determined by NuSTAR. These results show that, in contrast to the traditional orientation-based AGN unification model, the nature and covering factor of the absorbing gas and dust around AGNs evolve over time and must be connected to physical processes in the AGN environment. Future XRB synthesis models must allow for the redshift evolution of AGN spectral parameters. This approach may reveal fundamental connections between AGNs and their host galaxies.

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Section: The Impact Of the Compton-thick Fractionsupporting

confidence: 80%

The evolving X-ray spectrum of active galactic nuclei: evidence for an increasing reflection fraction with redshift

Avirett-Mackenzie

Ballantyne

2019

Monthly Notices of the Royal Astronomical Society

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“…We compare the Swift-BAT overall counts, as well as NuSTAR Extragalactic Survey overall number counts from Harrison et al (2016), with existing models. The NuSTAR Extragalactic Surveys are a wedding cake survey, and we look at three tiers in this work: UKIDSS Ultra Deep Survey (UDS; Masini et al 2018), COSMOS (Civano et al 2015), and Serendipitous Survey (Alexander et al 2013;. The details of each of these surveys are given in Table 2.…”

Section: The Observed Constraintsmentioning

confidence: 99%

The Accretion History of AGNs. I. Supermassive Black Hole Population Synthesis Model

Ananna

Treister

Urry

et al. 2019

ApJ

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106

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As matter accretes onto the central supermassive black holes in active galactic nuclei (AGNs), X-rays are emitted. We present a population synthesis model that accounts for the summed X-ray emission from growing black holes; modulo the efficiency of converting mass to X-rays, this is effectively a record of the accreted mass. We need this population synthesis model to reproduce observed constraints from X-ray surveys: the X-ray number counts, the observed fraction of Compton-thick AGNs [log (N H /cm −2 )>24], and the spectrum of the cosmic X-ray background (CXB), after accounting for selection biases. Over the past decade, X-ray surveys by XMM-Newton, Chandra, NuSTAR, and Swift-BAT have provided greatly improved observational constraints. We find that no existing X-ray luminosity function (XLF) consistently reproduces all these observations. We take the uncertainty in AGN spectra into account and use a neural network to compute an XLF that fits all observed constraints, including observed Compton-thick number counts and fractions. This new population synthesis model suggests that, intrinsically, 50%±9% (56% ± 7%) of all AGNs within z;0.1 (1.0) are Compton-thick.

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“…Recently, Masini et al (2018) estimated the Compton-think fraction of Compton-thick sources, using NuSTAR observations in the UKIDSS Ultra deep field. They find an observed Compton-thick fraction of 8.4 ± 2% in the 8-24 keV band at a flux of 2.7×10 −14 erg cm −2 s −1 .…”

Section: The Intrinsic Fraction Of Compton-thick Agnmentioning

confidence: 99%

NuSTARobservations of heavily obscuredSwift/BAT AGNs: Constraints on the Compton-thick AGNs fraction

Georgantopoulos

Akylas

2019

A&A

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The evolution of the accretion history of the Universe has been studied in unprecedented detail owing to recent X-ray surveys performed by Chandra and XMM-Newton. A missing piece of information is the most heavily obscured or Compton-thick AGN which evade detection even in X-ray surveys owing to their extreme hydrogen column densities which exceed 10 24 cm −2 . Recently, the all-sky hard X-ray survey performed by Swift/BAT brought a breakthrough allowing the detection of many of these AGN. This is because of its very high energy bandpass (14 − 195 keV) which helps to minimise attenuation effects. In our previous work, we have identified more than 50 candidate Compton-thick AGN in the local Universe, corresponding to an observed fraction of about 7% of the total AGN population. This number can be converted to the intrinsic Compton-thick AGN number density, only if we know their exact selection function. This function sensitively depends on the form of the Compton-thick AGN spectrum, that is the energy of their absorption turnover, photon-index and its cut-off energy at high energies, as well as the strength of the reflection component on the matter surrounding the nucleus. For example, the reflection component at hard energies 20-40 keV antagonises the number density of missing Compton-thick AGN in the sense that the stronger the reflection the easier these sources are detected in the BAT band. In order to constrain their number density, we analyse the spectra of 19 Compton-thick AGN which have been detected with Swift/BAT and have been subsequently observed with NuSTAR in the 3-80 keV band. We analyse their X-ray spectra using the MYTORUS models of Murphy and Yaqoob which properly take into account the Compton scattering effects. These are combined with physically motivated Comptonisation models which accurately describe the primary coronal X-ray emission. We derive absorbing column densities which are consistent with those derived by the previous Swift/BAT analyses. We estimate the coronal temperatures to be roughly between 25 and 80 keV corresponding to high energy cut-offs roughly between 75 and 250 keV. Furthermore, we find that the majority of our AGN lacks a strong reflection component in the 20-40 keV band placing tighter constraints on the intrinsic Compton-thick AGN fraction. Combining these results with our X-ray background synthesis models, we estimate a Compton-thick AGN fraction in the local Universe of ≈ 20 ± 3 % relative to the type-II AGN population .

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The NuSTAR Extragalactic Surveys: Source Catalog and the Compton-thick Fraction in the UDS Field

Cited by 37 publications

References 67 publications

The evolving X-ray spectrum of active galactic nuclei: evidence for an increasing reflection fraction with redshift

The evolving X-ray spectrum of active galactic nuclei: evidence for an increasing reflection fraction with redshift

The Accretion History of AGNs. I. Supermassive Black Hole Population Synthesis Model

NuSTARobservations of heavily obscuredSwift/BAT AGNs: Constraints on the Compton-thick AGNs fraction

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