The coronal properties of Active Galactic Nuclei at intermediate redshift: results from the SUBWAYS sample

Supermassive black holes (SMBHs), with masses in the range 1e6-1e10 M⊙, are commonly found at the centers of galaxies. When active, they power Active Galactic Nuclei (AGN), where accreting matter forms a disk emitting in the ultraviolet (UV) and a surrounding corona producing X-ray emission via inverse Compton scattering. This study investigates for the first time the coronal properties of a statistically rapresentative sample of 23 luminous AGN observed in the SUBWAYS campaign (SUpermassive Black holes Winds in XrAYs), targeting quasars at redshifts 0.1 < z < 0.4 with bolometric luminosities in the range 2 e44 < L(bol)(erg/s) < 2e46. High-quality X-ray spectra from XMM-Newton, complemented by NuSTAR data extending up to 40-50 keV rest-frame energy, allow for a detailed characterization of coronal parameters, including high-energy cut-off, electron temperature and optical depth. The study of both the soft and hard X-ray bands provides a comprehensive understanding of the regions near SMBH. The soft X-ray band (0.3-2 keV) focuses on modeling the soft excess using a warm corona model. A hot corona model is employed to describe the emission for the hard X-ray band. The analysis reveals a median warm corona temperature of ∼ 0.30 keV, consistent with literature values (0.1-1 keV) and an optically thick plasma with τ ∼ 20 − 40. The hot corona exhibits a median high-energy cut-off of ∼ 60 keV, significantly lower than the 100 − 150 keV, typically found in local Seyferts, and an optical depth of τ ∼ 5 − 10, at odd with an optically thin plasma. These findings suggest that more luminous AGN may host cooler and thicker coronae. Moreover, modeling of Comptonization processes indicates a deviation from the standard Ecut = (3 ÷ 2)kTe relation, instead favoring Ecut = 4kTe. These findings provide new insights into the physical conditions of AGN coronae.