The Lockman-SpReSO Project: A Deep X-ray Spectral View of a FIR-selected AGN Population

We present a detailed X-ray spectral analysis of the active galactic nucleus (AGN) population in the Lockman-SpReSO project, a multiwavelength campaign of FIR sources in the Lockman Hole field. Using deep XMM-Newton observations cross-matched with FIR-selected galaxies, we characterize 94 AGNs based on their X-ray spectral properties. The sample is distributed over a large redshift range of z = 0.07 − 5, and reaches a flux limit of 5 × 10−16 erg s−1 cm−2 in the 0.3 − 10 keV band. We model the X-ray spectra using absorbed power-law, reflection, and soft excess components to estimate intrinsic column densities (NH), rest-frame 2 − 10 keV luminosities, and iron line equivalent widths (EW). Additionally, we included an advanced model fitting for Compton-thick AGNs (CT-AGNs) using the XCLUMPY model. Our results show an increase in the fraction of obscured AGNs toward higher redshifts, including the identification of one strong and two borderline CT-AGN candidates with NH ≳ 1024 cm−2. Soft excess emission is detected in 10 AGNs, with an average blackbody temperature of 0.12 ± 0.02 keV. We also detect the X-ray Baldwin effect in both obscured and unobscured populations, and we found a strong correlation between the torus angular width (σtor), dust covering factor (fcov), and X-ray luminosity, described by fcov = ( − 0.1 ± 0.01) × log (L2 − 10 keV/(1044 erg s−1)) + (0.65 ± 0.01), supporting the receding torus scenario. While consistent with deep X-ray surveys, the FIR selection favours the identification of dusty star-forming host galaxies and heavily obscured AGNs.