The NuSTAR Extragalactic Surveys: First Direct Measurements of the > 10 keV X-Ray Luminosity Function for Active Galactic Nuclei at z > 0.1

Creators: Aird, J.; Harrison, F. A.; Baloković, M.; Brightman, M.; Forster, K.; Grefenstette, B. W.; Madsen, K. K.

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 N_H ~ 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.

Additional Information

© 2015 The American Astronomical Society. Received 2015 July 31; accepted 2015 October 8; published 2015 December 10. This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NUSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). We acknowledge financial support from: ERC Advanced Grant FEEDBACK at the University of Cambridge (J.A., A.C.F.); a COFUND Junior Research Fellowship from the Institute of Advanced Study, Durham University (J.A.); the Science and Technology Facilities Council (STFC) grants ST/I001573/1 (D.M.A. and A.D.M.), ST/K501979/1 (G.B.L.), and ST/J003697/1 (P.G.); the Leverhulme Trust (D.M.A.); the Caltech Kingsley Visitor Program (D.M.A., A.C.); NSF award AST 1008067 (D.R.B.); NASA grants 11-ADAP11-0218 and GO3-14150C (F.C.); an Alfred P. Sloan Research Fellowship and a Dartmouth Class of 1962 Faculty Fellowship (R.C.H.); CONICYT-Chile grants Basal-CATA PFB-06/2007 (F.E.B., E.T.); FONDECYT 1141218 (F.E.B.) and 1120061 (E.T.); "EMBIGGEN" Anillo ACT1101 (F.E.B., E.T.); the Ministry of Economy, Development, and Tourisms Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS (F.E.B.); NASA NuSTAR subcontract 44A-1092750 and NASA ADP grant NNX10AC99G (W.N.B., B.L.); ASI/INAF grant I/037/12/0011/13 (A.C., L.Z.); and NASA Earth and Space Science Fellowship Program grant NNX14AQ07H (M.B.).

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