4XMM high-z AGN

For sources without spectroscopic data (~80%), we estimated the photometric redshifts using both spectral energy distribution (SED) fitting and machine-learning algorithms. Among the ~65000 X-ray sources in the 4XMM-DES-VHS area, we ended up with 833 z>=3.5 AGN (11% having spec-z information) with a high level of reliability, along with a fraction of outliers of {eta}<=10%. The sample completeness is ~90%, driven by the depth of DES data.

Only ~10% of the X-ray selected AGN are also optical QSOs and vice versa. Our findings indicate an observed absorbed fraction (logN_H_[cm^-2^]>=23) of 20-40% for the X-ray AGN, significantly higher than that of optical QSOs. X-ray AGN exhibit fainter observed optical magnitudes and brighter mid-IR magnitudes than optical QSOs.

Their median rest-frame SED shapes differ notably with optical QSOs being dominated by AGN emission in the UV-optical wavelengths. While the median SEDs of X-ray AGN suggest extinction in the UV-optical range, individual sources exhibit a wide range of spectral shapes, indicating significant diversity within the population. This analysis supports the notion that X-ray-selected and optically selected AGN represent distinct and complementary populations.