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

Here, 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 $$\sim {10}^{25}\,{\mathrm{cm}}^{-2}$$. 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 $$5\times {10}^{-15}\,\lesssim $$ S(3–8 keV)/$$\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,\lesssim \,{10}^{-12}$$ probed by NuSTAR. In the hard 8–24 keV band NuSTAR probes fluxes over the range $$2\times {10}^{-14}\,\lesssim $$ S(8–24 keV)/$$\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}\,\lesssim \,{10}^{-12}$$, 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) gsim 10-11 $$\mathrm{erg}\,{{\rm{s}}}^{-1}\,{\mathrm{cm}}^{-2}$$), reflecting the evolution of the AGN population between the Swift/BAT local ($$z\lt 0.1$$) sample and NuSTAR's $$z\sim 1$$ 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.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [4] ; ORCiD logo [5] ; ORCiD logo [6] ; ORCiD logo [4] ; ORCiD logo [7] ; ORCiD logo [8] ; ORCiD logo [9] ; ORCiD logo [10] ;  [1] ; ORCiD logo [11] ;  [1] ;  [12] ; ORCiD logo [13] ; ORCiD logo [14] ;  [15] ;  [4] ;  [1] more »; ORCiD logo [16] ;  [17] ; ORCiD logo [1] ;  [18] ; ORCiD logo [19] ;  [13] ;  [20] ;  [21] ; ORCiD logo [11] ; ORCiD logo [1] ;  [1] ; ORCiD logo [1] ; ORCiD logo [18] ;  [22] ;  [23] ; ORCiD logo [22] ; ORCiD logo [1] ;  [24] ; ORCiD logo [25] ;  [13] ; ORCiD logo [26] ;  [27] ;  [26] ;  [12] « less
  1. California Inst. of Technology (CalTech), Pasadena, CA (United States). Cahill Center for Astronomy and Astrophysics
  2. Univ. of Cambridge (United Kingdom). Inst. of Astronomy; Durham Univ. (United Kingdom). Centre of Extragalactic Astronomy, Dept. of Physics
  3. Yale Univ., New Haven, CT (United States). Yale Center for Astronomy and Astrophysics
  4. Durham Univ. (United Kingdom). Centre of Extragalactic Astronomy, Dept. of Physics
  5. Univ. of Sheffield (United Kingdom). Dept. of Physics and Astronomy
  6. Georgia Inst. of Technology, Atlanta, GA (United States). Center for Relativistic Astrophysics, School of Physics
  7. California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  8. Clemson Univ., SC (United States). Kinard Lab of Physics, Dept. of Physics and Astronomy
  9. Univ. de Toulouse (France). Inst. de Recherche en Astrophysique et Planetologie
  10. Pontifical Catholic Univ. of Chile, Santiago (Chile). Inst. de Astrofisica, Facultad de Fisica; Millennium Inst. of Astrophysics, Santiago (Chile); Space Science Inst., Boulder, CO (United States)
  11. Pennsylvania State Univ., University Park, PA (United States). Dept of Astronomy and Astrophysics; Pennsylvania State Univ., University Park, PA (United States). Inst. for Gravitation and the Cosmos; Pennsylvania State Univ., University Park, PA (United States). Dept. of Physics
  12. Univ. of California, Berkeley, CA (United States). Space Sciences Lab.
  13. Technical Univ. of Denmark, Lyngby (Denmark). DTU Space-National Space Inst.
  14. Istituto Nazionale di Astrofisica (INAF), Bologna (Italy). Osservatorio Astronomico di Bologna
  15. Univ. of California, Berkeley, CA (United States). Space Sciences Lab.; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  16. Univ. of Southampton (United Kingdom). School of Physics & Astronomy
  17. ASI Science Data Center (ASDC), Rome (Italy)
  18. Columbia Univ., New York, NY (United States). Columbia Astrophysics Lab.
  19. Dartmouth College, Hanover, NH (United States). Dept. of Physics and Astronomy
  20. Hiroshima Univ. (Japan). Dept. of Physical Science
  21. SLAC National Accelerator Lab., Menlo Park, CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology
  22. ASI Science Data Center (ASDC), Rome (Italy); Istituto Nazionale di Astrofisica (INAF), Monte Porzio Catone (Italy). Osservatorio Astronomico di Roma
  23. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  24. Univ. de Concepcion (Chile). Dept. de Astronomia
  25. California Inst. of Technology (CalTech), Pasadena, CA (United States). Cahill Center for Astronomy and Astrophysics; California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
  26. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  27. Istituto Nazionale di Astrofisica (INAF), Monte Porzio Catone (Italy). Osservatorio Astronomico di Roma
Publication Date:
Grant/Contract Number:
AC02-76SF00515; NNG08FD60C
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 831; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE; National Aeronautics and Space Administration (NASA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies; active galaxies; nuclei galaxies; Seyfert surveys X-rays; diffuse background
OSTI Identifier:
1360168