The WISSH quasar project. XII. X-ray view of the most luminous quasi-stellar objects at Cosmic Noon
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arXiv
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2025
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| author | Agosti, C. Degli Vignali, C. Piconcelli, E. Zappacosta, L. Bertola, E. Middei, R. Saccheo, I. Vietri, G. Vito, F. Bongiorno, A. Bischetti, M. Bruni, G. Carniani, S. Cresci, G. Feruglio, C. Salvestrini, F. Travascio, A. Gaspari, M. Glikman, E. Kammoun, E. Lanzuisi, G. Laurenti, M. Miniutti, G. Pinto, C. Testa, V. Tombesi, F. Tortosa, A. Fiore, F. |
| author_facet | Agosti, C. Degli Vignali, C. Piconcelli, E. Zappacosta, L. Bertola, E. Middei, R. Saccheo, I. Vietri, G. Vito, F. Bongiorno, A. Bischetti, M. Bruni, G. Carniani, S. Cresci, G. Feruglio, C. Salvestrini, F. Travascio, A. Gaspari, M. Glikman, E. Kammoun, E. Lanzuisi, G. Laurenti, M. Miniutti, G. Pinto, C. Testa, V. Tombesi, F. Tortosa, A. Fiore, F. |
| contents | To improve our knowledge of nuclear emission in luminous QSOs at Cosmic Noon, we studied the X-ray emission of the WISE/SDSS-selected hyper-luminous (WISSH) QSO sample: 85 broad-line AGN with $L_{bol}>few\times 10^{47}\,erg\,s^{-1}$ at $z\sim 2-4$. Our aim is to characterise their X-ray spectra and explore relations between X-ray luminosity and other bands, comparing powerful QSOs with the general AGN population. We performed spectral analysis for about half of the sample; 16 sources were analysed via their hardness ratio; for the others we estimated their intrinsic luminosity $L_{2-10\,keV}$. Only 8 sources are undetected. We report a large dispersion in $L_{2-10\,keV}$ despite the narrow distribution of $L_{bol}$, $L_{2500\,Å}$ and $λL_{6\,μm}$ (about one-third of the sources classified as X-ray weak). This suggests differences in X-ray corona and accretion flow physics between hyper-luminous and less powerful AGN. X-ray photon index distribution is consistent with that of lower-$z$, lower-$L_{bol}$ AGN, and does not depend on the Eddington ratio ($λ_{Edd}$) or X-ray weakness. Most WISSH QSOs with intrinsic absorption estimates show little to no obscuration ($N_H \le 5\times 10^{22}\,cm^{-2}$). Among the obscured sources we find blue QSOs without broad absorption lines within the "forbidden region" of the $Log(N_H)-Log(λ_{Edd})$ plane, typically occupied by dust-reddened QSOs and associated with intense feedback. We confirm a correlation between $L_{2-10\,keV}$ and CIV line blueshift, a tracer of nuclear ionized outflows. Multi-wavelength data and complete X-ray coverage enabled the investigation of the disk-corona interplay at the highest luminosity regimes. The broad distribution of bolometric correction and X-ray - to - optical index suggest caution when using $L_{bol}$, $L_{2500\,Å}$ or $L_{6\,μm}$ as direct X-ray proxy for individual luminous QSOs. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2509_08055 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The WISSH quasar project. XII. X-ray view of the most luminous quasi-stellar objects at Cosmic Noon Agosti, C. Degli Vignali, C. Piconcelli, E. Zappacosta, L. Bertola, E. Middei, R. Saccheo, I. Vietri, G. Vito, F. Bongiorno, A. Bischetti, M. Bruni, G. Carniani, S. Cresci, G. Feruglio, C. Salvestrini, F. Travascio, A. Gaspari, M. Glikman, E. Kammoun, E. Lanzuisi, G. Laurenti, M. Miniutti, G. Pinto, C. Testa, V. Tombesi, F. Tortosa, A. Fiore, F. Astrophysics of Galaxies High Energy Astrophysical Phenomena To improve our knowledge of nuclear emission in luminous QSOs at Cosmic Noon, we studied the X-ray emission of the WISE/SDSS-selected hyper-luminous (WISSH) QSO sample: 85 broad-line AGN with $L_{bol}>few\times 10^{47}\,erg\,s^{-1}$ at $z\sim 2-4$. Our aim is to characterise their X-ray spectra and explore relations between X-ray luminosity and other bands, comparing powerful QSOs with the general AGN population. We performed spectral analysis for about half of the sample; 16 sources were analysed via their hardness ratio; for the others we estimated their intrinsic luminosity $L_{2-10\,keV}$. Only 8 sources are undetected. We report a large dispersion in $L_{2-10\,keV}$ despite the narrow distribution of $L_{bol}$, $L_{2500\,Å}$ and $λL_{6\,μm}$ (about one-third of the sources classified as X-ray weak). This suggests differences in X-ray corona and accretion flow physics between hyper-luminous and less powerful AGN. X-ray photon index distribution is consistent with that of lower-$z$, lower-$L_{bol}$ AGN, and does not depend on the Eddington ratio ($λ_{Edd}$) or X-ray weakness. Most WISSH QSOs with intrinsic absorption estimates show little to no obscuration ($N_H \le 5\times 10^{22}\,cm^{-2}$). Among the obscured sources we find blue QSOs without broad absorption lines within the "forbidden region" of the $Log(N_H)-Log(λ_{Edd})$ plane, typically occupied by dust-reddened QSOs and associated with intense feedback. We confirm a correlation between $L_{2-10\,keV}$ and CIV line blueshift, a tracer of nuclear ionized outflows. Multi-wavelength data and complete X-ray coverage enabled the investigation of the disk-corona interplay at the highest luminosity regimes. The broad distribution of bolometric correction and X-ray - to - optical index suggest caution when using $L_{bol}$, $L_{2500\,Å}$ or $L_{6\,μm}$ as direct X-ray proxy for individual luminous QSOs. |
| title | The WISSH quasar project. XII. X-ray view of the most luminous quasi-stellar objects at Cosmic Noon |
| topic | Astrophysics of Galaxies High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2509.08055 |