We report on the results of active galactic nuclei (AGNs) detection by NuSTAR
performed in three extragalactic survey fields (COSMOS, UDS, ECDFS) in three
hard bands, namely H1 (8-16 keV), H2 (16-24 keV) and VH (35-55 keV). The
aggregated area of the surveys is ∼2.7 deg2. While a large number of
sources is detected in the H1 band (72 at the 97% level of reliability), the
H2 band directly probing close to the peak of the Cosmic X-ray Background (CXB)
returns four significant detections, and two tentative, although not
significant, detections are found in the VH band. All the sources detected
above 16 keV are also detected at lower energies. We compute the integral
number counts for sources in such bands, which show broad consistency with
population synthesis models of the CXB. We furthermore identify two
Compton-thick AGNs, one in the COSMOS field, associated with a hard and faint
Chandra source, and one in the UDS field, never detected in the X-ray band
before. Both sources are at the same redshift z∼1.25, which shifts their
Compton-hump into the H1 band, and were previously missed in the usually
employed NuSTAR bands, confirming the potential of using the H1 band to
discover obscured AGNs at z>1 in deep surveys.Comment: 12 pages, 5 figures, accepted for publication in The Astrophysical
Journa