Effect of Extinction on Quasar Luminosity Distances Determined from UV and X-Ray Flux Measurements

Abstract

In Khadka et al., a sample of X-ray-detected reverberation-mapped quasars was presented and applied for the comparison of cosmological constraints inferred using two well-established relations in active galactic nuclei—the X-ray/UV luminosity (L X –L UV) relation and the broad-line region radius–luminosity (R–L) relation. L X –L UV and R–L luminosity distances to the same quasars exhibit a distribution of their differences that is generally asymmetric and positively shifted for the six cosmological models we consider. We demonstrate that this behavior can be interpreted qualitatively as arising as a result of the dust extinction of UV/X-ray quasar emission. We show that the extinction always contributes to the nonzero difference between L X –L UV-based and R–L-based luminosity distances and we derive a linear relationship between the X-ray/UV color index E X−UV and the luminosity-distance difference, which also depends on the value of the L X –L UV relation slope. Taking into account the median and the peak values of the luminosity-distance difference distributions, the average X-ray/UV color index falls in the range of E ¯ X − UV = 0.03 – 0.28 mag for the current sample of 58 sources. This amount of extinction is typical for the majority of quasars and can be attributed to the circumnuclear and interstellar media of host galaxies. After applying the standard hard X-ray and far-UV extinction cuts, heavily extincted sources are removed but overall the shift toward positive values persists. The effect of extinction on luminosity distances is more pronounced for the L X –L UV relation since the extinction of UV and X-ray emissions both contribute.

High Redshift $\Lambda$Cdm Cosmology: To Bin or Not to Bin?

“…In particular, a nonconstant Ω m is either a problem with the ΛCDM model or the data set, here the Risaliti-Lusso QSO data set [72]. If the problem is on the data set side, this adds credence to claims that QSOs are not standardisable [74][75][76][77][78][79][80].…”

“…Evidently, ( 13) is a working assumption. It is the subject of a growing body of work in the cosmology literature either questioning [74][75][76][77][78][79][80] or refining the Risaliti-Lusso prescription [100,101]. 9 In particular, it has been argued in [80] that the Risaliti-Lusso QSOs are impacted by extinction, but this effect may not be large enough to explain the discrepancy seen in the Hubble diagram [102].…”

“…It is the subject of a growing body of work in the cosmology literature either questioning [74][75][76][77][78][79][80] or refining the Risaliti-Lusso prescription [100,101]. 9 In particular, it has been argued in [80] that the Risaliti-Lusso QSOs are impacted by extinction, but this effect may not be large enough to explain the discrepancy seen in the Hubble diagram [102]. Here, it is worth stressing that QSOs represent emerging cosmological probes [103] and considerable work remains to turn the proposal into standardisable candles on par with Type Ia SNe, where developments span 3 decades.…”

“…Our interest here is exploring high redshift observables that have different systematics to QSOs. In addition, while the standardisability of QSOs has been called into question [74][75][76][77][78][79][80], similar tests on GRBs standardised through the Amati correlation [113] have been presented with a relatively clean bill of health [81]. More precisely, the authors of [81] claim that GRBs being standardisable, nonetheless, the full sample of 220 GRBs leads to a value of the ΛCDM parameter Ω m that is discrepant at the > 2σ level with the Planck-ΛCDM cosmology.…”

“…The point of this letter is that the larger values of Ω m and Ω m h 2 preferred by the Risaliti-Lusso QSOs are also preferred by JWST, at least at the level of qualitative comparison. Since the standardisability of the Risaliti-Lusso QSOs has been openly challenged [74][75][76][77][78][79][80], we identify a gamma-ray burst (GRB) data set, which apparently passes standardisable candle tests failed by QSOs [81], that exhibits the same trend. Along the way, we explain the limitations of prevailing methods for determining frequentist confidence intervals from profile likelihoods and comment on fresh methodology [82] (see also [83,84]) that generalises existing methods.…”