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

Abstract

Motivated by the idea of using quasars as standardizable candles for cosmology, we examine the relation between X-ray (at 2 keV, $L_{2keV}$) and ultraviolet (at 2500 Angstrom, $L_{2500}$) monochromatic luminosities of quasars using a sample of 2414 X-ray sources from the SRG/eROSITA all-sky survey cross-matched with the Sloan Digital Sky Survey data release 16 quasar catalogue (SDSS DR16Q), at redshifts between 0.5 and 2.5. These objects are bright both in X-rays and in the optical, so that the sample is characterized by nearly 100% statistical completeness. We have developed a new method for determining the $L_{2keV}-L_{2500}$ relation, which consistently takes into account (i) X-ray and UV flux limited object selection, (ii) X-ray and UV variability of quasars, and (iii) the decreasing space density of quasars with increasing luminosity. Assuming a linear relation between $l_{\mathrm{X}}\equiv \log (L_{2keV}/[\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{H}{\mathrm{z}}^{-1}])$ and $l_{\mathrm{UV}}\equiv \log (L_{2500}/[\mathrm{erg}{\mathrm{s}}^{-1}\mathrm{H}{\mathrm{z}}^{-1}])$, we find the slope, $\gamma =0.69\pm 0.02$ (hereafter all uncertainties are quoted at the 68% confidence level), and normalization, $l_{\mathrm{X}}=26.47\pm 0.02$ at $l_{\mathrm{UV}}=30.5$, of the $L_{2keV}$ ($L_{2500}$) dependence. These values are not substantially different from the results of previous studies. A key novel aspect of our work is allowance for intrinsic scatter (which adds to the dispersion induced by quasar variability and flux measurement uncertainties) of the $L_{2keV}-L_{2500}$ relation in both variables, i.e. in X-ray and UV luminosity. The intrinsic X-ray scatter (${\sigma }_{\mathrm{intX}}^2=0.063\pm 0.005$) strongly dominates over the UV one (${\sigma }_{\mathrm{intUV}}^2=0.002_{-0.002}^{+0.003}$). Further studies should seek to explain this behaviour in terms of accretion onto supermassive black holes and orientation of quasars with respect to the observer.

29 pages, 5 tables, 18 figures

References in corpus (39)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Improved Cosmological Constraints from New, Old and Combined Supernova Datasets
• The Pantheon+ Analysis: Cosmological Constraints
• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• Dark Energy Survey Year 3 Results: Cosmological Constraints from Galaxy Clustering and Weak Lensing
• DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations
• The eROSITA X-ray telescope on SRG
• Modeling the Time Variability of SDSS Stripe 82 Quasars as a Damped Random Walk
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• Active Galactic Nuclei: what's in a name?
• BAT AGN Spectroscopic Survey - V. X-ray properties of the Swift/BAT 70-month AGN catalog
• 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
• CRATES: An All-Sky Survey of Flat-Spectrum Radio Sources
• The SRG X-ray orbital observatory, its telescopes and first scientific results
• The 5th edition of the Roma-BZCAT. A short presentation
• The Early Data Release of the Dark Energy Spectroscopic Instrument
• 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 Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope -- Data Release 3
• Correlated X-ray/Optical Variability in the Quasar MR2251-178
• Intensive disc-reverberation mapping of Fairall 9: 1st year of Swift & LCO monitoring
• Luminosity Function from dedicated SDSS-III and MMT data of quasars in 0.7<z<4.0 selected with a new approach
• Gravitationally lensed quasars in Gaia -- IV. 150 new lenses, quasar pairs, and projected quasars
• Quasar standardization: Overcoming Selection Biases and Redshift Evolution
• Quasars as standard candles II: The non linear relation between UV and X-ray emission at high redshifts
• Ensemble X-ray variability of Active Galactic Nuclei. II. Excess Variance and updated Structure Function
• Measuring Quasar Variability with Pan-STARRS1 and SDSS
• A long term study of AGN X-ray variability. Structure function analysis on a ROSAT-XMM quasar sample
• The Chandra view of the relation between X-ray and UV emission in quasars
• Redshift Evolution and Non-Universal Dispersion of Quasar Luminosity Correlation
• Flares in the changing look AGN Mrk 590. I: The UV response to X-ray outbursts suggests a more complex reprocessing geometry than a standard disk
• Wavelength Dependences of the Optical/UV and X-ray Luminosity Correlations of Quasars
• A catalog of candidate double and lensed quasars from Gaia and WISE data
• 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
• DULAG: A DUal and Lensed AGN candidate catalog with GMP method
• Revisiting the X-ray-to-UV relation of Quasars in the era of all-sky surveys
• The X-ray$-$UV Luminosity Relation of eROSITA Quasars