X-ray View of Hyper-Luminous Quasars at z = 2 ~ 4: the WISSH project

At the cosmic noon (z≈2-4), hyper-luminous quasars (HyLQSOs) shine at L_bol>10^47 erg/s and the most energetic multiphase winds are predicted to be ejected. These are the most efficient feedback governing AGN-galaxy co-evolution. The WISSH project aims at investigating the multi-wavelength properties of 85 WISE/SDSS selected type 1 (i.e. unobscured) HyLQSOs at the cosmic noon, to study their spectral and wind properties. We focuse on the X-ray emission of this sample, processing Chandra/XMM-Newton data. The slope of the primary power-law (Γ) and possible intrinsic column density (N_H ) are measured. Γ is broadly consistent with the expected range ~1.8-2. About 24% of the sources for which N_H can be estimated exhibits N_H≥10^22 cm^(-2). The observed quasars have an intrinsic 2-10 keV luminosity L_X≈10^(43-46) erg/s. Knowing the bolometric and monochromatic 2500 Å (L_2500 ) luminosities, we derive the bolometric correction (k_bol ) and X-ray - to - optical index (α_OX ). In the L_bol-k_bol and L_2500-α_OX, WISSH QSOs arrange anomalously with respect to literature relations, i.e. covering a wide range of k_bol and α_OX for a given bolometric or monochromatic luminosity. This evidence highlights a possible different coupling in the accretion disk - corona. The offset of the observed α_OX from the expected one (from literature relations) defines ∆(α_OX). Having ∆(α_OX )<-0.2, ~22% of WISSH sources are “X-ray weak”, i.e. characterised by a lower relative contribution of the X-ray emission to L_bol compared to lower-luminous samples. From M_BH, Eddington ratio is evaluated as λ_Edd≈0.1-3. Previously found correlations with Γ do not seem to work at λ_Edd ~ 1, where data are highly dispersed. In the λ_Edd-N_H plane, WISSH blue quasars occupy the “forbidden region” (i.e. high-λ_Edd/high-N_H), identified by Fabian+08 and typically associated with red sources (E(B-V)>0.15).