Standardizing reverberation-measured C iv time-lag quasars, and using them with standardized Mg ii quasars to constrain cosmological parameters

We use 38 C iv quasar (QSO) reverberation-mapped observations, which span eight orders of magnitude in luminosity and the redshift range 0.001064 <= z <= 3.368, to simultaneously constrain cosmological-model and QSO radius-luminosity (R-L) relation parameters in six cosmological models, using an improved technique that more correctly accounts for the asymmetric errors bars of the time-lag measurements. We find that R-L relation parameters are independent of the cosmological models used in the analysis and so the R-L relation can be used to standardize the C iv QSOs. The C iv QSO cosmological constraints are consistent with those from Mg ii QSOs, allowing us to derive joint C iv + Mg ii QSO cosmological constraints which are consistent with currently accelerated cosmological expansion, as well as consistent with cosmological constraints derived using better-established baryon acoustic oscillation (BAO) and Hubble parameter [H(z)] measurements. When jointly analysed with H(z) + BAO data, current C iv + Mg ii QSO data mildly tighten current H(z) + BAO data cosmological constraints.

Automated summary

In this study, we used a large sample of C iv quasar (QSO) observations to simultaneously constrain cosmological models and QSO radius-luminosity (R-L) relation parameters. The results show that the R-L relation parameters are independent of the cosmological models, indicating that the R-L relation can be used to standardize C iv QSOs.