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The NuSTAR Extragalactic Surveys: The Number Counts of Active Galactic Nuclei and the Resolved Fraction of the Cosmic X-ray Background

Harrison, F. A. and Baloković, M. and Brightman, M. and Forster, K. and Grefenstette, B. W. and Madsen, K. K. and Mao, P. H. and Miyasaka, H. and Rana, V. and Walton, D. (2016) The NuSTAR Extragalactic Surveys: The Number Counts of Active Galactic Nuclei and the Resolved Fraction of the Cosmic X-ray Background. Astrophysical Journal, 831 (2). Art. No. 185. ISSN 0004-637X. doi:10.3847/0004-637X/831/2/185.

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We present the 3–8 keV and 8–24 keV number counts of active galactic nuclei (AGNs) identified in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic surveys. NuSTAR has now resolved 33%–39% of the X-ray background in the 8–24 keV band, directly identifying AGNs with obscuring columns up to ~10^(25) cm^(-2). In the softer 3–8 keV band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range 5 x 10^(-15) ≾S(3–8 keV)/erg s^(-1) cm^(-2) ≾10^(-12) probed by NuSTAR. In the hard 8–24 keV band NuSTAR probes fluxes over the range 2 x 10^(-14) ≾ S(8–24 keV)/ erg s^(-1) cm^(-2) ≾ 10^_12), a factor ~100 fainter than previous measurements. The 8–24 keV number counts match predictions from AGN population synthesis models, directly confirming the existence of a population of obscured and/or hard X-ray sources inferred from the shape of the integrated cosmic X-ray background. The measured NuSTAR counts lie significantly above simple extrapolation with a Euclidian slope to low flux of the Swift/BAT 15–55 keV number counts measured at higher fluxes (S(15–55 keV) ≳10^(−11) erg s^(-1) cm^(-2)), reflecting the evolution of the AGN population between the Swift/BAT local (z < 0.1) sample and NuSTAR's z ~ 1 sample. CXB synthesis models, which account for AGN evolution, lie above the Swift/BAT measurements, suggesting that they do not fully capture the evolution of obscured AGNs at low redshifts.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Harrison, F. A.0000-0003-2992-8024
Baloković, M.0000-0003-0476-6647
Brightman, M.0000-0002-8147-2602
Forster, K.0000-0001-5800-5531
Grefenstette, B. W.0000-0002-1984-2932
Madsen, K. K.0000-0003-1252-4891
Miyasaka, H.0000-0002-8074-4186
Rana, V.0000-0003-1703-8796
Walton, D.0000-0001-5819-3552
Additional Information:© 2016 The American Astronomical Society. Received 2015 October 29; revised 2016 August 23; accepted 2016 August 24; published 2016 November 7. This work was supported under NASA Contract No. NNG08FD60C, and 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). J.A. acknowledges support from ERC Advanced Grant FEEDBACK at the University of Cambridge and a COFUND Junior Research Fellowship from the Institute of Advanced Study, Durham University.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
European Research Council (ERC)FEEDBACK
Durham UniversityUNSPECIFIED
Subject Keywords:galaxies: active – galaxies: nuclei – galaxies: Seyfert – surveys – X-rays: diffuse background – X-rays: galaxies
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-23
Issue or Number:2
Record Number:CaltechAUTHORS:20160128-144830164
Persistent URL:
Official Citation:F. A. Harrison et al 2016 ApJ 831 185
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:64061
Deposited By: Ruth Sustaita
Deposited On:28 Jan 2016 23:07
Last Modified:10 Nov 2021 23:25

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