Do reverberation-measured Hβ quasars provide a useful test of cosmology?

We use 118 H beta quasar (QSO) observations in the redshift range 0.0023 <= z <= 0.89 to simultaneously constrain cosmological model parameters and QSO 2-parameter radius-luminosity (R-L) relation parameters in six different cosmological models. We find that the R-L relation parameters for these QSOs are independent of the assumed cosmology so these QSOs seem to be standardizable through the R-L relation (although there is a complication that might render this untrue). Cosmological constraints obtained using these QSOs are weak, more favour currently decelerated cosmological expansion, and typically are in similar to 2 sigma tension with those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements. Extending the R-L relation to a 3-parameter one to try to correct for the accretion rate effect does not result in a reduction of the cosmological constraints discrepancy nor does it result in the hoped-for significant reduction of the intrinsic scatter of the R-L relation.

Automated summary

We utilize 118 H beta quasar observations to investigate the cosmological model parameters and the radius-luminosity relation parameters. The results show that the assumed cosmology does not affect the relation parameters, indicating that the quasars can be standardized through this relation. However, the cosmological constraints obtained are weak and favor a currently decelerating expansion. Extending the relation does not reduce the discrepancy in cosmological constraints.