[Paper Review] X-Ray Evidence Against the Hypothesis that the Hyper-Luminous z=6.3 Quasar J0100+2802 is Lensed

Thomas Connor, Daniel Stern+2 more|arXiv (Cornell University)|Nov 10, 2021

Astrophysical Phenomena and Observations56 references9 citations

TL;DR

This study challenges the hypothesis that the hyper-luminous z=6.3 quasar J0100+2802 is gravitationally lensed with a magnification of ~450, using X-ray data from XMM-Newton. It finds that the quasar's X-ray luminosity is inconsistent with such extreme magnification, as it would require the source to be anomalously X-ray faint—contradicting known quasar scaling relations and implying a fundamental inconsistency with the broader population of high-redshift quasars.

ABSTRACT

The $z=6.327$ quasar SDSS J010013.02+280225.8 (hereafter J0100+2802) is believed to be powered by a black hole more massive than $10^{10}\ { m M}_\odot$, making it the most massive black hole known in the first billion years of the Universe. However, recent high-resolution ALMA imaging shows four structures at the location of this quasar, potentially implying that it is lensed with a magnification of $\mu\sim450$ and thus its black hole is significantly less massive. Furthermore, for the underlying distribution of magnifications of $z\gtrsim6$ quasars to produce such an extreme value, theoretical models predict that a larger number of quasars in this epoch should be lensed, implying further overestimates of early black hole masses. To provide an independent constraint on the possibility that J0100+2802 is lensed, we re-analyzed archival XMM-Newton observations of the quasar and compared the expected ratios of X-ray luminosity to rest-frame UV and IR luminosities. For both cases, J0100+2802's X-ray flux is consistent with the no-lensing scenario; while this could be explained by J0100+2802 being X-ray faint, we find it does not have the X-ray or optical spectral features expected for an X-ray faint quasar. Finally, we compare the overall distribution of X-ray fluxes for known, typical $z\gtrsim6$ quasars. We find a $3\sigma$ tension between the observed and predicted X-ray-to-UV flux ratios when adopting the magnification probability distribution required to produce a $\mu=450$ quasar.

Motivation & Objective

• To test the hypothesis that the hyper-luminous z=6.3 quasar J0100+2802 is gravitationally lensed with a magnification of ~450, as suggested by ALMA imaging.
• To assess whether the X-ray luminosity of J0100+2802 is consistent with the lensed scenario by comparing it to established X-ray/UV and X-ray/IR luminosity relations.
• To evaluate whether the required lensing probability distribution for a µ~450 quasar is compatible with the observed X-ray properties of the broader z>6 quasar population.
• To determine whether J0100+2802 exhibits spectral characteristics typical of X-ray faint quasars, which would be expected if it were lensed and intrinsically faint.
• To quantify the tension between the lensing hypothesis and established scaling relations in high-redshift quasars, particularly the αOX and LX–νL6µm relations.

Proposed method

• Re-analyzed archival XMM-Newton X-ray observations of J0100+2802 using updated calibration and SAS v19.0.0, with source extraction via xmmextractor and careful background region selection.
• Computed rest-frame X-ray luminosity (L2−10 keV) and compared it to UV (L2500) and infrared (νL6µm) luminosities to test consistency with the Lusso & Risaliti (2016) αOX relation and Stern (2015) LX–νL6µm relation.
• Quantified the statistical significance of deviations from these scaling relations using the intrinsic scatter of the relations and standard error on the mean.
• Simulated the expected distribution of ∆αOX values for z>6 quasars under the lensing hypothesis, assuming a luminosity function with β ≥ 3.7 to produce a µ~450 event.
• Used probabilistic lensing models from Pacucci & Loeb (2020) to estimate the probability of magnification, extrapolating beyond µ=10 in log(P(≥µ))–log(µ) space with a 10% conservative slope reduction.
• Smoothed observed and simulated ∆αOX distributions with Gaussian kernels matching individual measurement uncertainties to assess statistical consistency.

Experimental results

Research questions

• RQ1 Is the X-ray luminosity of J0100+2802 consistent with a magnification of ~450, as implied by ALMA imaging?
• RQ2 Does J0100+2802 exhibit the spectral characteristics of a typical X-ray faint quasar, which would be expected if it were intrinsically faint due to lensing?
• RQ3 If J0100+2802 is magnified by µ~450, is the resulting population of lensed z>6 quasars consistent with the observed X-ray/UV luminosity relation (αOX) at lower redshifts?
• RQ4 What is the statistical tension between the lensing hypothesis and the scaling relations of high-redshift quasars, particularly in the X-ray band?
• RQ5 Does the required luminosity function slope (β ≥ 3.7) to produce a µ~450 quasar conflict with observed quasar properties in the X-ray band?

Key findings

• If J0100+2802 were magnified by µ~450, its αOX value would deviate from the Lusso & Risaliti (2016) relation by ∆αOX = −0.32, corresponding to a 3.5σ significance based on intrinsic scatter.
• The quasar's X-ray luminosity is inconsistent with the Stern (2015) LX–νL6µm relation, with a log(L2−10 keV) offset of −1.00, exceeding the range of all 155 quasars in the Stern sample (2.7σ significance).
• The spectral energy distribution of J0100+2802 does not show the optical and X-ray features characteristic of X-ray faint quasars, ruling out intrinsic X-ray faintness as a plausible explanation.
• Simulations show that if the lensing hypothesis is correct, the broader z>6 quasar population would need to be significantly more lensed than observed, leading to a >3σ tension with the Lusso & Risaliti αOX relation.
• The required luminosity function slope β ≥ 3.7 to produce a µ~450 quasar implies a population of lensed quasars that is inconsistent with the lack of observed X-ray evolution in high-redshift AGN up to z~6.
• The X-ray data provide strong independent evidence against the lensing hypothesis, as the observed X-ray properties of J0100+2802 are incompatible with the extreme magnification required by the ALMA interpretation.