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The NuSTAR Extragalactic survey : first direct measurements of the \gsim10 KeV x-ray luminosity function for active galactic nuclei at z > 0.1.

Aird, J. and Alexander, D.M. and Ballantyne, D.R. and Civano, F. and Del-Moro, A. and Hickox, R.C. and Lansbury, G.B. and Mullaney, J.R. and Bauer, F.E. and Brandt, W.N. and Comastri, A. and Fabian, A.C. and Gandhi, P. and Harrison, F.A. and Luo, B. and Stern, D. and Treister, E. and Zappacosta, L. and Ajello, M. and Assef, R. and Baloković, M. and Boggs, S.E. and Brightman, M. and Christensen, F.E. and Craig, W.W. and Elvis, M. and Forster, K. and Grefenstette, B.W. and Hailey, C.J. and Koss, M. and LaMassa, S.M. and Madsen, K.K. and Puccetti, S. and Saez, C. and Urry, C.M. and Wik, D.R. and Zhang, W. (2015) 'The NuSTAR Extragalactic survey : first direct measurements of the \gsim10 KeV x-ray luminosity function for active galactic nuclei at z > 0.1.', Astrophysical journal., 815 (1). p. 66.


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 ${N}_{{\rm{H}}}\sim {10}^{23-24}$ 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.

Item Type:Article
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Publisher statement:© 2015. The American Astronomical Society.
Date accepted:No date available
Date deposited:15 July 2016
Date of first online publication:10 December 2015
Date first made open access:No date available

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