2024A&A...691A.235T

One of the main open questions in the field of luminous (L_bol > 10⁴⁷ erg s^–1) quasars (QSOs) at z ≳ 6 is the rapid formation (< 1 Gyr) of their supermassive black holes (SMBHs). For this work we analysed the relation between the X-ray properties and other properties describing the physics and growth of both the accretion disc and the SMBH in QSOs at the Epoch of Reionization (EoR). The sample consists of 21 z > 6 QSOs, which includes 16 sources from the rapidly grown QSOs from the HYPERION sample and five other luminous QSOs with available high-quality archival X-ray data. We discovered a strong and statistically significant (> 3σ) relation between the X-ray continuum photon index (Γ) and the C IV disc wind velocity (v_C.IV) in z > 6 luminous QSOs, whereby the higher the v_C.IV, the steeper the Γ. This relation suggests a link between the disc-corona configuration and the kinematics of disc winds. Furthermore, we find evidence at > 2 - 3σ level that Γ and v_C.IV are correlated to the growth rate history of the SMBH. Although additional data are needed to confirm it, this result may suggest that, in luminous z > 6 QSOs, the SMBH predominantly grows via fast accretion rather than via initial high seed BH mass.