1. The NuSTAR Extragalactic Surveys: The Number Counts Of Active Galactic Nuclei And The Resolved Fraction Of The Cosmic X-ray Background
- Author
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Harrison, F. A, Aird, J, Civano, F, Lansbury, G, Mullaney, J. R, Ballentyne, D. R, Alexander, D. M, Stern, D, Ajello, M, Barret, D, Bauer, F. E, Balokovic, M, Brandt, W. N, Brightman, M, Boggs, S. E, Christensen, F. E, Comastri, A, Craig, W. W, Del Moro, A, Forster, K, Gandhi, P, Giommi, P, Grefenstette, B. W, Hailey, C. J, Hickox, R. C, Hornstrup, A, Kitaguchi, T, Koglin, J, Luo, B, Madsen, K. K, Mao, P. H, Miyasaka, H, Mori, K, Perri, M, Pivovaroff, M, Puccetti, S, Rana, V, Treister, E, Walton, D, Westergaard, N. J, Wik, D, Zappacosta, L, Zhang, W. W, and Zoglauer, A
- Subjects
Astrophysics - Abstract
We present the 3-8 kiloelectronvolts and 8-24 kiloelectronvolts number counts of active galactic nuclei (AGNs) identified in the Nuclear Spectroscopic Telescope Array (NuSTAR) extragalactic surveys. NuSTAR has now resolved 33 percent -39 percent of the X-ray background in the 8-24 kiloelectronvolts band, directly identifying AGNs with obscuring columns up to approximately 10 (exp 25) per square centimeter. In the softer 3-8 kiloelectronvolts band the number counts are in general agreement with those measured by XMM-Newton and Chandra over the flux range 5 times 10 (exp -15) less than or approximately equal to S (3-8 kiloelectronvolts) divided by ergs per second per square centimeter less than or approximately equal to 10 (exp -12) probed by NuSTAR. In the hard 8-24 kiloelectronvolts band NuSTAR probes fluxes over the range 2 times 10 (exp -14) less than or approximately equal to S (8-24 kiloelectronvolts) divided by ergs per second per square centimeter less than or approximately equal to 10 (exp -12), a factor approximately 100 times fainter than previous measurements. The 8-24 kiloelectronvolts 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/BAT15-55 kiloelectronvolts number counts measured at higher fluxes (S (15-55 kiloelectronvolts) less than or approximately equal to 10 (exp -11) ergs per second per square centimeter), reflecting the evolution of the AGN population between the Swift/BAT local (redshift is less than 0.1) sample and NuSTAR's redshift approximately equal to 1 sample. CXB (Cosmic X-ray Background) 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
- Published
- 2016
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