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

TL;DR

This study uses reverberation-mapped C IV quasars, combined with Mg II quasars, to improve constraints on cosmological parameters, confirming the accelerated expansion of the universe with a new, more accurate method.

Contribution

It introduces an improved technique for analyzing quasar time-lag data that accounts for asymmetric error bars, enabling the use of C IV QSOs as standard candles for cosmology.

Findings

C IV R-L relation parameters are independent of cosmological models.

C IV and Mg II QSOs provide consistent cosmological constraints.

Joint analysis with H(z) and BAO data mildly tightens constraints.

Abstract

We use 38 C IV quasar (QSO) reverberation-mapped (RM) observations, which span eight orders of magnitude in luminosity and the redshift range $0.001064 \leq z \leq 3.368$, 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 analyzed with $H(z)$ + BAO data, current C IV + Mg II QSO data mildly tighten current $H(z)$ + BAO data cosmological constraints.