To fully understand cosmic black hole growth we need to constrain the population of heavily obscured active galactic nuclei (AGN) at the peak of cosmic black hole growth ($z\sim$1-3). Sources with obscuring column densities higher than $\mathrm10^24$ atoms $\mathrmcm^-2$, called Compton-thick (CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, called the "Compton hump". We apply the recently developed Spectral Curvature (SC) method to high-redshift AGN (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 AGN 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 $\mathrm17^+19_-11\%$ (3/17) for sources with observed luminosity $\mathrm>5\times 10^43$ erg $\mathrms^-1$. In the Cosmological evolution survey (COSMOS), we find an observed CT fraction of $\mathrm15^+4_-3\%$ (40/272) or $\mathrm32\pm11 \%$ when corrected for the survey sensitivity. When comparing to low redshift AGN with similar X-ray luminosities, our results imply 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 AGN (z>1) for current (XMM-Newton) and future (eROSITA and ATHENA) X-ray missions.
Baronchelli, L., Koss, M., Schawinski, K., Cardamone, C., Civano, F., Comastri, A., et al. (2017). Inferring Compton-thick AGN candidates at z > 2 with Chandra using the >8 keV rest-frame spectral curvature. MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, 471(1), 364-372 [10.1093/mnras/stx1561].
Inferring Compton-thick AGN candidates at z > 2 with Chandra using the >8 keV rest-frame spectral curvature
Lanzuisi, G.Membro del Collaboration Group
;
2017
Abstract
To fully understand cosmic black hole growth we need to constrain the population of heavily obscured active galactic nuclei (AGN) at the peak of cosmic black hole growth ($z\sim$1-3). Sources with obscuring column densities higher than $\mathrm10^24$ atoms $\mathrmcm^-2$, called Compton-thick (CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, called the "Compton hump". We apply the recently developed Spectral Curvature (SC) method to high-redshift AGN (2I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.