The NuSTAR Extragalactic Surveys: The Number Counts of Active Galactic Nuclei and The Resolved Fraction of The Cosmic X-Ray Background
Journal Article
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· The Astrophysical Journal (Online)
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- California Inst. of Technology (CalTech), Pasadena, CA (United States). Cahill Center for Astronomy and Astrophysics
- Univ. of Cambridge (United Kingdom). Inst. of Astronomy; Durham Univ. (United Kingdom). Centre of Extragalactic Astronomy, Dept. of Physics
- Yale Univ., New Haven, CT (United States). Yale Center for Astronomy and Astrophysics
- Durham Univ. (United Kingdom). Centre of Extragalactic Astronomy, Dept. of Physics
- Univ. of Sheffield (United Kingdom). Dept. of Physics and Astronomy
- Georgia Inst. of Technology, Atlanta, GA (United States). Center for Relativistic Astrophysics, School of Physics
- California Inst. of Technology (CalTech), Pasadena, CA (United States). Jet Propulsion Lab.
- Clemson Univ., SC (United States). Kinard Lab of Physics, Dept. of Physics and Astronomy
- Univ. de Toulouse (France). Inst. de Recherche en Astrophysique et Planetologie
- 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)
- 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
- Univ. of California, Berkeley, CA (United States). Space Sciences Lab.
- Technical Univ. of Denmark, Lyngby (Denmark). DTU Space-National Space Inst.
- Istituto Nazionale di Astrofisica (INAF), Bologna (Italy). Osservatorio Astronomico di Bologna
- Univ. of California, Berkeley, CA (United States). Space Sciences Lab.; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Univ. of Southampton (United Kingdom). School of Physics & Astronomy
- ASI Science Data Center (ASDC), Rome (Italy)
- Columbia Univ., New York, NY (United States). Columbia Astrophysics Lab.
- Dartmouth College, Hanover, NH (United States). Dept. of Physics and Astronomy
- Hiroshima Univ. (Japan). Dept. of Physical Science
- SLAC National Accelerator Lab., Menlo Park, CA (United States). Kavli Inst. for Particle Astrophysics and Cosmology
- ASI Science Data Center (ASDC), Rome (Italy); Istituto Nazionale di Astrofisica (INAF), Monte Porzio Catone (Italy). Osservatorio Astronomico di Roma
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Univ. de Concepcion (Chile). Dept. de Astronomia
- 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.
- NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
- Istituto Nazionale di Astrofisica (INAF), Monte Porzio Catone (Italy). Osservatorio Astronomico di Roma
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.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States); SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
- Sponsoring Organization:
- European Research Council (ERC); National Aeronautics and Space Administration (NASA); USDOE; USDOE National Nuclear Security Administration (NNSA)
- Grant/Contract Number:
- AC02-76SF00515; AC52-07NA27344
- OSTI ID:
- 1360168
- Alternate ID(s):
- OSTI ID: 1876983
OSTI ID: 22868483
- Report Number(s):
- LLNL-JRNL-837151
- Journal Information:
- The Astrophysical Journal (Online), Journal Name: The Astrophysical Journal (Online) Journal Issue: 2 Vol. 831; ISSN 1538-4357
- Publisher:
- IOP PublishingCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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Wed Nov 09 23:00:00 EST 2016
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OSTI ID:22868483
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