2025/09/09 by Agosti, C. Degli, Vignali, C., Piconcelli, E. +25 · 1 citation
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2509.08055
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 Lbol>few× 1047 erg s-1 at z∼ 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 L2-10 keV. Only 8 sources are undetected. We report a large dispersion in L2-10 keV despite the narrow distribution of Lbol, L2500 Å and λL6 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-Lbol AGN, and does not depend on the Eddington ratio (λEdd) or X-ray weakness. Most WISSH QSOs with intrinsic absorption estimates show little to no obscuration (NH ≤ 5× 1022 cm-2). Among the obscured sources we find blue QSOs without broad absorption lines within the "forbidden region" of the Log(NH)-Log(λEdd) plane, typically occupied by dust-reddened QSOs and associated with intense feedback. We confirm a correlation between L2-10 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 Lbol, L2500 Å or L6 μm as direct X-ray proxy for individual luminous QSOs.