The NuSTAR Extragalactic Surveys: XRay Spectroscopic Analysis of the Bright Hardband Selected Sample
Abstract
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}}}^{1} {{cm}}^{2} in the multitiered NuSTAR extragalactic survey program. The sources span a redshift range z=0{}2.1 (median < z> =0.58). The spectral analysis is performed over the broad 0.524 keV energy range, combining NuSTAR with Chandra and/or XMMNewton 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 ({N}_{{{H}}}), reflection parameter ({\boldsymbol{R}}), and 1040 keV luminosity ({L}_{{{X}}}). Heavily obscured ({log}[{N}_{{{H}}}/{{cm}}^{2}]≥slant 23) and Comptonthick (CT; {log}[{N}_{{{H}}}/{{cm}}^{2}]≥slant 24) AGN constitute ∼25% (1517 sources) and ∼23% (12 sources) of the sample, respectively. The observed {N}_{{{H}}} distribution agrees fairly well with predictions of cosmic Xray background populationsynthesis models (CXBPSM). We estimate the intrinsic fraction of AGN as a function of {N}_{{{H}}}, accounting for the bias against obscured AGN in a fluxselected sample. The fraction of CT AGN relative to {log}[{N}_{{{H}}}/{{cm}}^{2}]=20{}24 AGN is poorly constrained, formally in the range 256% (90% upper limit of 66%). We derived a fraction (f _{abs}) of obscured AGN ({log}[{N}_{{{H}}}/{{cm}}^{2}]=22{}24) as a function of {L}_{{{X}}} in agreement with CXBPSM and previous z< 1 Xray determinations. Furthermore, f _{abs} at z=0.1{}0.5 and {log}({L}_{{{x}}}/{erg} {{{s}}}^{1})≈ 43.6{}44.3 agrees with observational measurements/trends obtained over larger redshift intervals. We report a significant anticorrelation of R with {L}_{{{X}}} (confirmed by our companion paper on stacked spectra) with considerable scatter around the median R values.
 Publication:

The Astrophysical Journal
 Pub Date:
 February 2018
 DOI:
 10.3847/15384357/aaa550
 arXiv:
 arXiv:1801.04280
 Bibcode:
 2018ApJ...854...33Z
 Keywords:

 galaxies: active;
 surveys;
 Xrays: galaxies;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 Comments: 38 pages, 17 figures, 8 tables. Accepted for publication in ApJ