Inferring Compton-thick AGN candidates at z > 2 with Chandra using the >8 keV rest-frame spectral curvature
Date Issued
2017
Author(s)
Baronchelli, L.
•
Koss, M.
•
Schawinski, K.
•
Cardamone, C.
•
Civano, F.
•
•
Elvis, M.
•
•
•
Ricci, C.
•
Salvato, M.
•
Trakhtenbrot, B.
•
Treister, E.
Abstract
To fully understand cosmic black hole growth, we need to constrain the population of heavily obscured active galactic nuclei (AGNs) at the peak of cosmic black hole growth (z ∼1-3). Sources with obscuring column densities higher than 1024 atoms cm-2, called Compton-thick (CT) AGNs, can be identified by excess X-ray emission at ∼20-30 keV, called the 'Compton hump'. We apply the recently developed Spectral Curvature (SC) method to high-redshift AGNs (2 < z < 5) detected with Chandra. This method parametrizes the characteristic 'Compton hump' feature cosmologically redshifted into the X-ray band at observed energies <10 keV. We find good agreement in CT AGNs found using the SC method, and bright sources fit using their full spectrum with X-ray spectroscopy. In the Chandra Deep Field-South, we measure a CT fraction of 17^{+19}_{-11} per cent (3/17) for sources with observed luminosity >5 × 1043erg s-1. In the Cosmological Evolution Survey (COSMOS), we find an observed CT fraction of 15^{+4}_{-3} per cent (40/272) or 32 ± 11 per cent when corrected for the survey sensitivity. When comparing to low redshift AGNs with similar X-ray luminosities, our results imply that the CT AGN fraction is consistent with having no redshift evolution. Finally, we provide SC equations that can be used to find high-redshift CT AGNs (z > 1) for current (XMM-Newton) and future (eROSITA and ATHENA) X-ray missions.
Volume
471
Issue
1
Start page
364
Issn Identifier
0035-8711
Ads BibCode
2017MNRAS.471..364B
Rights
open.access
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