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

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 (L-X - L-UV) relations and the implication of these relations for cosmological parameter estimation. By simultaneously determining R - L or L-X - L-UV relation parameters and cosmological parameters in six different cosmological models, we find that both R - L and L-X - L-UV relations are standardizable but provide only weak cosmological parameter constraints, with L-X - L-UV relation data favouring larger current non-relativistic matter density parameter omega(m0) values than R - L relation data and most other available data. We derive L-X - L-UV and R - L luminosity distances for each of the sources in the six cosmological models and find that L-X - L-UV relation luminosity distances are shorter than R - L relation luminosity distances as well as standard flat ?CDM model luminosity distances. This explains why L-X - L-UV relation QSO data favour larger omega(m0) 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 L-X - L-UV relation can be used as a cosmological probe.

Automated summary

In this study, measurements of 59/58 quasars are used to compare the radius-luminosity (R - L) and X-ray-UV luminosity (L-X - L-UV) relations and their implications for cosmological parameter estimation. Results show that both R - L and L-X - L-UV relations are standardizable but provide weak constraints on cosmological parameters. Moreover, L-X - L-UV relation data tend to favor larger values of the non-relativistic matter density parameter compared to R - L relation data and other measurements. It is concluded that more research is needed to determine if the L-X - L-UV relation can be used as a cosmological probe.