The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample

L. Zappacosta, A. Comastri, F. Civano, S. Puccetti, F. Fiore, J. Aird, A. Del Moro, G. B. Lansbury, G. Lanzuisi, A. Goulding, J. R. Mullaney, D. Stern, M. Ajello, D. M. Alexander, D. R. Ballantyne, F. E. Bauer, W. N. Brandt, C. T.J. Chen, D. Farrah, F. A. HarrisonP. Gandhi, L. Lanz, A. Masini, S. Marchesi, C. Ricci, E. Treister

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16 Scopus citations

Abstract

We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting fluxof S (8-24 keV) = 7×10-14 erg s-1 cm-1 in the multi-tiered NuSTAR extragalactic survey program. The sourcesspan a redshift range z = 0-2.1 (median 〈z〈 = 0.58). The spectral analysis is performed over the broad 0.5-24 keVenergy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical andphysically motivated models. This constitutes the largest sample of AGN selected at >10 keV to behomogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters suchas photon index, column density (NH), reflection parameter (R), and 10-40 keV luminosity (LX). Heavily obscured(log NH cm 23[ -2]) and Compton-thick (CT; log N cm 24 H[ -2]) AGN constitute ∼25% (15-17 sources) and∼2-3% (1-2 sources) of the sample, respectively. The observed NH distribution agrees fairly well with predictionsof cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGNas a function of NH, accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CTAGN relative to log NH cm 20 24[ -2] = - AGN is poorly constrained, formally in the range 2-56% (90% upperlimit of 66%). We derived a fraction ( fabs) of obscured AGN (log NH cm 22 24[-2] = -) as a function of LX inagreement with CXBPSM and previous z < 1 X-ray determinations. Furthermore, fabs at z = 0.1-0.5 andlog Lx erg s 43.6 44.3( -1) - agrees with observational measurements/trends obtained over larger redshiftintervals. We report a significant anti-correlation of R with LX (confirmed by our companion paper on stackedspectra) with considerable scatter around the median R values.

Original languageEnglish (US)
Article number33
JournalAstrophysical Journal
Volume854
Issue number1
DOIs
StatePublished - Feb 10 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

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