A deep look at nearby heavily obscured AGNs with NuSTAR and XMM-Newton

The cosmic X-ray background (CXB), the diffuse X-ray emission observed between 0.5 keV and 300 keV, is thought to be mainly produced by obscured and unobscured active galactic nuclei (AGN). Compton-thick (CT-) AGNs (with absorbing column density NH >10²⁴ cm^-2) are responsible for ~30% of the CXB at its peak and expected to be numerous. However, as of today CT-AGNs have never been detected in large numbers, their observed fraction in the local universe being ~5-10%, significantly below the predictions of different CXB models (~20%-30%). I will present a deep observation of two candidate CT-AGNs, selected using an effective technique reported by our group two years ago, using the unprecedented-quality data from NuSTAR and XMM-Newton, which allows us to have a better understanding of the physics of the obscuration process in AGNs.