THE NuSTAR EXTRAGALACTIC SURVEYS: The NUMBER COUNTS of ACTIVE GALACTIC NUCLEI and the RESOLVED FRACTION of the COSMIC X-RAY BACKGROUND
Del Moro, A
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Harrison, F., Aird, J., Civano, F., Lansbury, G., Mullaney, J., Ballantyne, D., Alexander, D., et al. (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. 185)https://doi.org/10.3847/0004-637X/831/2/185
© 2016. The American Astronomical Society. All rights reserved. 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 . 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 S(3-8 keV)/ probed by NuSTAR. In the hard 8-24 keV band NuSTAR probes fluxes over the range S(8-24 keV)/, 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 ), reflecting the evolution of the AGN population between the Swift/BAT local () sample and NuSTAR's 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.
External DOI: https://doi.org/10.3847/0004-637X/831/2/185
This record's URL: https://www.repository.cam.ac.uk/handle/1810/261173