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The NuSTAR extragalactic survey: first direct measurements of the >~10 KeV x-ray luminosity function for active galactic nuclei at z>0.1

The NuSTAR extragalactic survey: first direct measurements of the >~10 KeV x-ray luminosity function for active galactic nuclei at z>0.1
The NuSTAR extragalactic survey: first direct measurements of the >~10 KeV x-ray luminosity function for active galactic nuclei at z>0.1
We present the first direct measurements of the rest-frame 10–40 keV X-ray luminosity function (XLF) of active galactic nuclei (AGNs) based on a sample of 94 sources at 0.1 < z < 3, selected at 8–24 keV energies from sources in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic survey program. Our results are consistent with the strong evolution of the AGN population seen in prior, lower-energy studies of the XLF. However, different models of the intrinsic distribution of absorption, which are used to correct for selection biases, give significantly different predictions for the total number of sources in our sample, leading to small, systematic differences in our binned estimates of the XLF. Adopting a model with a lower intrinsic fraction of Compton-thick sources and a larger population of sources with column densities NH ~ 1023-24 cm-2 or a model with stronger Compton reflection component (with a relative normalization of R ~ 2 at all luminosities) can bring extrapolations of the XLF from 2–10 keV into agreement with our NuSTAR sample. Ultimately, X-ray spectral analysis of the NuSTAR sources is required to break this degeneracy between the distribution of absorbing column densities and the strength of the Compton reflection component and thus refine our measurements of the XLF. Furthermore, the models that successfully describe the high-redshift population seen by NuSTAR tend to over-predict previous, high-energy measurements of the local XLF, indicating that there is evolution of the AGN population that is not fully captured by the current models.
galaxies, active, evolution, X-rays
1538-4357
1-13
Aird, J.
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Alexander, D.M.
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Ballantyne, D.R.
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Civano, F.
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Del-Moro, A.
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Hickox, R.C.
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Lansbury, G.B.
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Mullaney, J.R.
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Bauer, F.E.
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Brandt, W.N.
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Comastri, A.
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Fabian, A.C.
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Gandhi, P.
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Harrison, F.A.
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Luo, B.
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Stern, D.
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Treister, E.
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Zappaosta, L.
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Ajello, M.
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Assef, R.
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Balokovic, M.
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Boggs, S.E.
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Brightman, M.
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Christensen, F.E.
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Craig, W.W.
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Elvis, M.
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Forster, K.
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Grefenstette, B.W.
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Hailey, C.J.
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Koss, M.
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LaMassa, S.M.
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Madsen, K.K.
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Puccetti, S.
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Saez, C.
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Urry, C.M.
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Wik, D.R.
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Zhang, W.
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Aird, J.
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Alexander, D.M.
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Ballantyne, D.R.
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Civano, F.
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Del-Moro, A.
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Hickox, R.C.
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Lansbury, G.B.
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Mullaney, J.R.
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Bauer, F.E.
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Brandt, W.N.
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Comastri, A.
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Fabian, A.C.
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Gandhi, P.
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Harrison, F.A.
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Luo, B.
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Stern, D.
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Treister, E.
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Zappaosta, L.
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Ajello, M.
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Assef, R.
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Balokovic, M.
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Boggs, S.E.
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Brightman, M.
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Christensen, F.E.
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Craig, W.W.
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Elvis, M.
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Forster, K.
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Grefenstette, B.W.
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Hailey, C.J.
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Koss, M.
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LaMassa, S.M.
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Madsen, K.K.
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Puccetti, S.
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Saez, C.
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Urry, C.M.
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Wik, D.R.
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Zhang, W.
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Aird, J., Alexander, D.M., Ballantyne, D.R., Civano, F., Del-Moro, A., Hickox, R.C., Lansbury, G.B., Mullaney, J.R., Bauer, F.E., Brandt, W.N., Comastri, A., Fabian, A.C., Gandhi, P., Harrison, F.A., Luo, B., Stern, D., Treister, E., Zappaosta, L., Ajello, M., Assef, R., Balokovic, M., Boggs, S.E., Brightman, M., Christensen, F.E., Craig, W.W., Elvis, M., Forster, K., Grefenstette, B.W., Hailey, C.J., Koss, M., LaMassa, S.M., Madsen, K.K., Puccetti, S., Saez, C., Urry, C.M., Wik, D.R. and Zhang, W. (2015) The NuSTAR extragalactic survey: first direct measurements of the >~10 KeV x-ray luminosity function for active galactic nuclei at z>0.1. The Astrophysical Journal, 815 (66), 1-13. (doi:10.1088/0004-637X/815/1/66).

Record type: Article

Abstract

We present the first direct measurements of the rest-frame 10–40 keV X-ray luminosity function (XLF) of active galactic nuclei (AGNs) based on a sample of 94 sources at 0.1 < z < 3, selected at 8–24 keV energies from sources in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic survey program. Our results are consistent with the strong evolution of the AGN population seen in prior, lower-energy studies of the XLF. However, different models of the intrinsic distribution of absorption, which are used to correct for selection biases, give significantly different predictions for the total number of sources in our sample, leading to small, systematic differences in our binned estimates of the XLF. Adopting a model with a lower intrinsic fraction of Compton-thick sources and a larger population of sources with column densities NH ~ 1023-24 cm-2 or a model with stronger Compton reflection component (with a relative normalization of R ~ 2 at all luminosities) can bring extrapolations of the XLF from 2–10 keV into agreement with our NuSTAR sample. Ultimately, X-ray spectral analysis of the NuSTAR sources is required to break this degeneracy between the distribution of absorbing column densities and the strength of the Compton reflection component and thus refine our measurements of the XLF. Furthermore, the models that successfully describe the high-redshift population seen by NuSTAR tend to over-predict previous, high-energy measurements of the local XLF, indicating that there is evolution of the AGN population that is not fully captured by the current models.

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More information

Accepted/In Press date: 8 October 2015
Published date: 10 December 2015
Keywords: galaxies, active, evolution, X-rays
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 400034
URI: https://eprints.soton.ac.uk/id/eprint/400034
ISSN: 1538-4357
PURE UUID: e79d422b-ca20-4da6-a48a-31e32e839029
ORCID for P. Gandhi: ORCID iD orcid.org/0000-0003-3105-2615

Catalogue record

Date deposited: 07 Sep 2016 10:14
Last modified: 07 Aug 2018 00:29

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Contributors

Author: J. Aird
Author: D.M. Alexander
Author: D.R. Ballantyne
Author: F. Civano
Author: A. Del-Moro
Author: R.C. Hickox
Author: G.B. Lansbury
Author: J.R. Mullaney
Author: F.E. Bauer
Author: W.N. Brandt
Author: A. Comastri
Author: A.C. Fabian
Author: P. Gandhi ORCID iD
Author: F.A. Harrison
Author: B. Luo
Author: D. Stern
Author: E. Treister
Author: L. Zappaosta
Author: M. Ajello
Author: R. Assef
Author: M. Balokovic
Author: S.E. Boggs
Author: M. Brightman
Author: F.E. Christensen
Author: W.W. Craig
Author: M. Elvis
Author: K. Forster
Author: B.W. Grefenstette
Author: C.J. Hailey
Author: M. Koss
Author: S.M. LaMassa
Author: K.K. Madsen
Author: S. Puccetti
Author: C. Saez
Author: C.M. Urry
Author: D.R. Wik
Author: W. Zhang

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