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To fully understand cosmic black hole growth we need to constrain thepopulation of heavily obscured active galactic nuclei (AGN) at the peak ofcosmic black hole growth ($z\sim$1-3). Sources with obscuring column densitieshigher than $\mathrm{10^{24}}$ atoms $\mathrm{cm^{-2}}$, called Compton-thick(CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, calledthe "Compton hump". We apply the recently developed Spectral Curvature (SC)method to high-redshift AGN (2<z<5) detected with Chandra. This methodparametrizes the characteristic "Compton hump" feature cosmologicallyredshifted into the X-ray band at observed energies <10 keV. We find goodagreement in CT AGN found using the SC method and bright sources fit usingtheir full spectrum with X-ray spectroscopy. In the Chandra deep field south,we measure a CT fraction of $\mathrm{17^{+19}_{-11}\%}$ (3/17) for sources withobserved luminosity $\mathrm{>5\times 10^{43}}$ erg $\mathrm{s^{-1}}$. In theCosmological evolution survey (COSMOS), we find an observed CT fraction of$\mathrm{15^{+4}_{-3}\%}$ (40/272) or $\mathrm{32\pm11 \%}$ when corrected forthe survey sensitivity. When comparing to low redshift AGN with similar X-rayluminosities, our results imply the CT AGN fraction is consistent with havingno redshift evolution. Finally, we provide SC equations that can be used tofind high-redshift CT AGN (z>1) for current (XMM-Newton) and future (eROSITAand ATHENA) X-ray missions.

Inferring Compton-thick AGN candidates at z>2 with Chandra using the >8 keV restframe spectral curvature