Baronchelli, L.L.BaronchelliKoss, M.M.KossSchawinski, K.K.SchawinskiCardamone, C.C.CardamoneCivano, F.F.CivanoCOMASTRI, AndreaAndreaCOMASTRIElvis, M.M.ElvisLANZUISI, GiorgioGiorgioLANZUISIMARCHESI, STEFANOSTEFANOMARCHESIRicci, C.C.RicciSalvato, M.M.SalvatoTrakhtenbrot, B.B.TrakhtenbrotTreister, E.E.Treister2020-08-282020-08-2820170035-8711http://hdl.handle.net/20.500.12386/26966To 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 10<SUP>24</SUP> atoms cm<SUP>-2</SUP>, 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 × 10<SUP>43</SUP>erg s<SUP>-1</SUP>. 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.STAMPAenArticle10.1093/mnras/stx15612-s2.0-85045913985000408211700020https://academic.oup.com/mnras/article/471/1/364/38923732017MNRAS.471..364BFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation