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

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

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


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.R. Ballantyne

F.E. Bauer

W.N. Brandt

C.-T.J. Chen

D. Farrah

F.A. Harrison

P. Gandhi

L. Lanz

A. Masini

S. Marchesi

C. Ricci

E. Treister


A Del-Moro


We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S 8 24 keV 7 10 = ´ -14 (– ) erg s cm - - 1 2 in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z = 0 2.1 – (median ázñ = 0.58). The spectral analysis is performed over the broad 0.5–24 keV energy range, combining NuSTAR with Chandra and/or XMM-Newton data and employing empirical and physically motivated models. This constitutes the largest sample of AGN selected at >10 keV to be homogeneously spectrally analyzed at these flux levels. We study the distribution of spectral parameters such as photon index, column density (NH), reflection parameter (R), and 10–40 keV luminosity (LX). Heavily obscured (log cm 2 NH 3 [ ] -2  ) and Compton-thick (CT; log cm 24 NH [ ] -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 predictions of cosmic X-ray background population-synthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of NH, accounting for the bias against obscured AGN in a flux-selected sample. The fraction of CT AGN relative to log cm 20 2 NH 4 [ ]– -2 = AGN is poorly constrained, formally in the range 2–56% (90% upper limit of 66%). We derived a fraction ( fabs) of obscured AGN (log cm 22 2 NH 4 [ ]– -2 = ) as a function of LX in agreement with CXBPSM and previous z < 1 X-ray determinations. Furthermore, fabs at z = 0.1 0.5 – and log erg s 43.6 44. Lx 3 ( )– -1 » agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anti-correlation of R with LX (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.

Journal Article Type Article
Acceptance Date Dec 29, 2017
Online Publication Date Feb 8, 2018
Publication Date Feb 8, 2018
Deposit Date Mar 1, 2018
Publicly Available Date Mar 1, 2018
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 854
Issue 1
Article Number 33
Public URL


Published Journal Article (1.9 Mb)

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© 2018. The American Astronomical Society. All rights reserved.

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