Quasar UV/X-ray relation luminosity distances are shorter than reverberation-measured radius–luminosity relation luminosity distances

Abstract

We use measurements of 59/58 quasars (QSOs), over a redshift range 0.0041 ≤ z ≤ 1.686, to do a comparative study of the radius–luminosity (R − L) and X-ray−UV luminosity (LX − LUV) relations and the implication of these relations for cosmological parameter estimation. By simultaneously determining R − L or LX − LUV relation parameters and cosmological parameters in six different cosmological models, we find that both R − L and LX − LUV relations are standardizable but provide only weak cosmological parameter constraints, with LX − LUV relation data favoring larger current non-relativistic matter density parameter Ωm0 values than R − L relation data and most other available data. We derive LX − LUV and R − L luminosity distances for each of the sources in the six cosmological models and find that LX − LUV relation luminosity distances are shorter than R − L relation luminosity distances as well as standard flat ΛCDM model luminosity distances. This explains why LX − LUV relation QSO data favor larger Ωm0 values than do R − L relation QSO data or most other cosmological measurements. While our sample size is small and only spans a small z range, these results indicate that more work is needed to determine whether the LX − LUV relation can be used as a cosmological probe.

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

“…In Khadka et al (2023), we showed that this is in agreement with the tendency for luminosity distances based on L X -L UV relation data to have a mean value smaller than luminosity distances based on R-L relation data for the same QSOs. The median L X -L UV relation luminosity-distance values, on the other hand, are mostly larger except for the flat and non-flat XCDM models.…”

“…For such a sample, in principle, both L X -L UV and R-L relations should be applicable. To this goal, we provided a sample of 58 X-ray-detected reverberation-mapped Mg II QSOs in Khadka et al (2023), from which we measured both the L X -L UV relation and the R-L relation parameter values that are consistent with values measured using larger samples. The sample was quite limited but we stress that for each of the sources we could determine the luminosity distance from these two methods independently.…”

“…Active galactic nuclei (AGN), especially bright quasars (quasi-stellar objects (QSOs); Karas et al 2021;Zajaček et al 2023), appear to be promising alternative probes due to their broad redshift coverage, ranging from the nearby Universe (z = 0.00106 for NGC4395; Brum et al 2019) to z ≈ 7.642 (J0313-1806; Wang et al 2021). For cosmological applications, so far three types of QSO data have been more widely utilized: (i) QSO angular size observations (Cao et al 2017;Ryan et al 2019;Cao et al 2020Cao et al , 2021aCao et al , 2021bLian et al 2021;Cao et al 2022b); (ii) data based on the nonlinear relation between QSO X-ray and UV luminosities, the L X -L UV relation (Risaliti & Lusso 2015Khadka & Ratra 2020a, 2020bLusso et al 2020;Li et al 2021;Colgáin et al 2022;Dainotti et al 2022;Hu & Wang 2022;Khadka & Ratra 2022;Petrosian et al 2022;Rezaei et al 2022;Khadka et al 2023); and (iii) data based on the correlation between the rest-frame broad-line region (BLR) time delay and the monochromatic luminosity, the R-L relation (Panda et al 2019a(Panda et al , 2019bMartínez-Aldama et al 2019;Khadka et al 2021bKhadka et al , 2022aKhadka et al , 2022bCzerny et al 2021;Zajaček et al 2021;Cao et al 2022cCao et al , 2023Cao & Ratra 2022;Panda 2022;Cao & Ratra 2023a;…”

Reducing the Uncertainty on the Hubble Constant up to 35% with an Improved Statistical Analysis: Different Best-fit Likelihoods for Type Ia Supernovae, Baryon Acoustic Oscillations, Quasars, and Gamma-Ray Bursts

“…Nevertheless, we have here described only the case of distance moduli for GRBs and the case of luminosities for QSOs to be consistent with the fitting procedure applied in our previous analysis. We prefer to construct the cosmological likelihood for QSOs with the logarithmic luminosities, as these are the quantities intrinsic to the RL relation (see Equation (10)) and also the ones that are commonly used for cosmological analyses in the literature (e.g., Khadka & Ratra 2020aLusso et al 2020;Bargiacchi et al 2022;Colgáin et al 2022a;Li et al 2022;Wang et al 2022;Cao & Ratra 2023;Khadka et al 2023;Lenart et al 2023). Thus, this approach allows an easier and more immediate comparison with results from other studies, without the need for taking into account possible differences in the respective methodologies.…”

Quasars: Standard Candles up to z = 7.5 with the Precision of Supernovae Ia

“…To this end, the community strives to reduce as much as possible the uncertainties on cosmological parameters and to find probes at intermediate redshifts which can be considered standard candles (Yonetoku et al 2004). Given the current interest of the community in quasars as reliable cosmological tools Dainotti et al 2022a; Bargiacchi et al 2022;Khadka et al 2023;Lenart et al 2023), we focus on the hunt for a gold sample for quasars, as already done for gamma-ray bursts (GRBs; Dainotti et al 2010Dainotti et al ,2013Dainotti et al ,2015Dainotti et al ,2016Dainotti et al ,2020Dainotti et al ,2021bDainotti et al ,2022bDainotti et al ,2022cDainotti et al ,2022dDainotti et al ,2023b. We propose an approach to the use of quasars as standard candles similar to the one done for SNe Ia 25 yr ago, but quasars are observed at much larger distances (up to z = 7.54).…”