HYPERION. Shedding light on the first luminous quasars: A correlation between UV disc winds and X-ray continuum

One of the main open questions in the field of luminous ($L_{\rm bol}>10^{47},\rm erg,s^{-1}$) quasars (QSOs) at $z \gtrsim 6$ 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 $\rm C,IV$ disc wind velocity ($v_{\rm C,IV}$) in $z>6$ luminous QSOs, whereby the higher the $v_{\rm C,IV}$, 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 $v_{\rm C,IV}$ 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.

💡 Research Summary

The paper presents a comprehensive multi‑wavelength study of the most luminous quasars (bolometric luminosities > 10⁴⁷ erg s⁻¹) at redshifts z > 6, aiming to uncover the physical link between the X‑ray emitting corona and the ultraviolet (UV) disc‑driven winds traced by the C IV broad emission line. The authors assemble a sample of 21 quasars, comprising 16 objects from the HYPERION programme—an XMM‑Newton multi‑year heritage campaign targeting the most rapidly growing high‑z quasars—and five additional luminous quasars with archival X‑ray observations of sufficient quality (≥30 net counts in the 0.3–7 keV band). All sources have published measurements of the C IV velocity shift (v_CIV) and, where available, the C IV rest‑frame equivalent width (REW_CIV).

X‑ray data reduction follows a uniform pipeline using SAS v18.0.0. Event files from EPIC‑pn and EPIC‑MOS are filtered for background flares, source extraction regions of 20″ (adjusted for crowded fields) are defined, and background regions are selected to avoid contaminating sources. Spectra are binned with the Kaastra‑Bleeker optimal grouping, which preserves spectral resolution while ensuring sufficient counts per bin for low‑count high‑z sources. Each spectrum is fitted with a simple absorbed power‑law model, yielding the photon index Γ (the slope of the primary X‑ray continuum) and, when possible, a high‑energy cut‑off E_cut. The authors report Γ values ranging from ~1.6 to ~2.5, systematically steeper than typical values for lower‑redshift quasars of comparable luminosity.

UV wind properties are taken from the literature. The C IV velocity shift is defined as the blueshift of the C IV line peak relative to the systemic redshift (usually measured from Mg II or