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

Abstract

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 $5\times 10^{-16}\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{c}{\mathrm{m}}^{-2}$ in the $0.3-10\mathrm{keV}$ band. We model the X-ray spectra using absorbed power-law, reflection, and soft excess components to estimate intrinsic column densities ($N_{\mathrm{H}}$), rest-frame $2-10\mathrm{keV}$ 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 $N_{\mathrm{H}}\gtrsim 10^{24}\mathrm{c}{\mathrm{m}}^{-2}$. Soft excess emission is detected in 10 AGNs, with an average blackbody temperature of $0.12\pm 0.02\mathrm{keV}$. 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 $({\sigma }_{\mathrm{tor}})$, dust covering factor $(f_{\mathrm{cov}})$, and X-ray luminosity, described by $f_{\mathrm{cov}}=(-0.1\pm 0.01)\times \log (L_{2-10\mathrm{keV}}/(10^{44}\mathrm{erg}{\mathrm{s}}^{-1}))+(0.65\pm 0.01)$, 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.

24 pages, 16 figures, accepted for publication in MNRAS