Revisiting the X-ray-to-UV relation of Quasars in the era of all-sky surveys

Abstract

The X-ray--to--UV relation of active galactic nuclei (AGNs), commonly parametrized via the monochromatic luminosities at $2500\mathring{A}$ and $2keV$, reflects the energetic interplay between the accretion disc and the X-ray-emitting corona, and is key for understanding accretion physics. Previous studies suggest that disc-dominated emission becomes more prominent with increasing optical luminosity. However, the redshift evolution of this relation remains debated, and a dependence on Eddington ratio, predicted by accretion flow models, is still observationally unconstrained. We revisit this relation using a large, nearly all-sky sample by combining the SDSS DR16Q QSO catalogue with X-ray data from XMM-Newton and the SRG/eROSITA All-Sky Survey DR1, yielding 136,745 QSOs at redshifts $0.5\le z<3.0$. We introduce a hierarchical Bayesian framework that treats X-ray detections and upper limits uniformly, enabling robust inference from both parametric and non-parametric models. We confirm a tight, sublinear $\log L_X(2\mathrm{keV})$-$\log L_{\nu }(2500\mathring{\mathrm{A}})$ correlation, but with a normalization at the lower end of previous estimates. Contrary to most literature results, we detect a mild but systematic redshift evolution: the relation flattens and its intrinsic scatter decreases at higher redshift. This trend is consistent with disc emission increasingly dominated by scattering and enhanced energy transfer to the X-ray corona, potentially indicating redshift evolution in the X-ray bolometric correction. We find no significant dependence on Eddington ratio, in tension with recent accretion flow models.

18+4 pages, 12+6 figures, Published at MNRAS

References in corpus (53)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The eROSITA X-ray telescope on SRG
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• Euclid. I. Overview of the Euclid mission
• The X-ray-to-Optical Properties of Optically-Selected Active Galaxies Over Wide Luminosity and Redshift Ranges
• The Sloan Digital Sky Survey Quasar Catalog: Sixteenth Data Release
• The LOFAR Two-metre Sky Survey -- V. Second data release
• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• The X-ray Properties of the Most-Luminous Quasars from the Sloan Digital Sky Survey
• The XMM-Newton serendipitous survey IX. The fourth XMM-Newton serendipitous source catalogue
• The SRG/eROSITA all-sky survey: First X-ray catalogues and data release of the western Galactic hemisphere
• The eROSITA Final Equatorial Depth Survey (eFEDS): The X-ray catalog
• Universal bolometric corrections for AGN over 7 luminosity decades
• X-CIGALE: fitting AGN/galaxy SEDs from X-ray to infrared
• A statistical test for Nested Sampling algorithms
• A Catalog of Quasar Properties from Sloan Digital Sky Survey Data Release 16
• Quasars as standard candles III. Validation of a new sample for cosmological studies
• The eROSITA Final Equatorial-Depth Survey (eFEDS): Catalog of galaxy clusters and groups
• Are Optically-Selected Quasars Universally X-Ray Luminous? X-Ray/UV Relations in Sloan Digital Sky Survey Quasars
• The UV Continuum of Quasars: Models and SDSS Spectral Slopes
• The NewAthena mission concept in the context of the next decade of X-ray astronomy
• A Full Year's Chandra Exposure on SDSS Quasars from the Chandra Multiwavelength Project
• The LOFAR Two-Metre Sky Survey (LoTSS): VI. Optical identifications for the second data release
• Quasars as standard candles II: The non linear relation between UV and X-ray emission at high redshifts
• Evolution of the X-ray Emission of Radio-Quiet Quasars
• The most luminous blue quasars at $3.0<z<3.3$. I. A tale of two X-ray populations
• The $L_{\mathrm{x}}$-$L_{\mathrm{uv}}$-$L_{\mathrm{radio}}$ relation and corona-disk-jet connection in optically selected radio-loud quasars
• Detecting clusters of galaxies and active galactic nuclei in an eROSITA all-sky survey digital twin
• Testing AGN outflow and accretion models with CIV and HeII emission line demographics in z=2 quasars
• The final SDSS-IV/SPIDERS X-ray point source spectroscopic catalogue
• X-ray spectroscopic survey of highly-accreting AGN
• A physical model for the broadband energy spectrum of X-ray illuminated accretion discs: fitting the spectral energy distribution of NGC 5548
• The Chandra view of the relation between X-ray and UV emission in quasars
• An X-ray selected catalog of extended galaxy clusters from the ROSAT All-Sky Survey (RXGCC)
• The SOUX AGN sample: Optical/UV/X-ray SEDs and the nature of the disc
• What controls the UV-to-X-ray continuum shape in quasars?
• The Time-Domain Spectroscopic Survey: Target Selection for Repeat Spectroscopy
• Data Release 1 of the Dark Energy Spectroscopic Instrument
• The RapidXMM Upper Limit Server: X-ray aperture photometry of the XMM-Newton archival observations
• A universal average spectral energy distribution for quasars from optical to extreme ultraviolet
• Prior-Informed AGN-Host Spectral Decomposition Using PyQSOFit
• NuSTAR Observations of Intrinsically X-ray Weak Quasar Candidates: An Obscuration-Only Scenario
• Black hole mass estimation using X-ray variability measurements in Seyfert galaxies
• Ensemble power spectral density of SDSS quasars in UV/optical bands
• Redshift-evolutionary X-ray and UV luminosity relation of quasars from Gaussian copula
• The SOUX AGN Sample: SDSS-XMM-Newton Optical, Ultraviolet and X-ray selected active galactic nuclei spanning a wide range of parameter space -- Sample definition
• Investigating the nuclear properties of highly accreting active galactic nuclei with XMM-Newton
• Quasars as Standard Candles V. Evaluation of a $\le$ 0.06 dex intrinsic dispersion in the LX-LUV relation
• The intrinsic X-ray luminosity distribution of an optically-selected SDSS quasar population
• Quasars as high-redshift standard candles
• Weakness of X-rays and Variability in High-redshift AGNs with Super-Eddington Accretion
• The WISSH quasar project. XII. X-ray view of the most luminous quasi-stellar objects at Cosmic Noon
• Searching for outflows in X-ray weak quasars

Cited by in corpus (1)

• SRG/eROSITA-SDSS view on the relation between X-ray and UV emission for quasars