Effects of heterogeneous data sets and time-lag measurement techniques on cosmological parameter constraints from MgII and CIV reverberation-mapped quasar data

TL;DR

This study assesses how heterogeneous quasar data sets and different time-lag measurement techniques influence cosmological parameter constraints derived from MgII and CIV reverberation-mapped quasars, emphasizing data quality over quantity.

Contribution

It demonstrates that increasing sample size alone does not improve constraints; data quality and measurement consistency are crucial for reliable cosmological inferences.

Findings

Adding lower-quality data increases differences between models.

Different time-delay methods have minimal impact on robust samples.

Sample quality cuts are essential for standardizable quasar data.

Abstract

Previously, we demonstrated that MgII and CIV reverberation-mapped quasars (RM QSOs) are standardizable and that the cosmological parameters inferred using the broad-line region radius-luminosity (R-L) relation are consistent with those determined from better-established cosmological probes. With more data expected from ongoing and future spectroscopic and photometric surveys, it is imperative to examine how new QSO data sets of varied quality, with their own specific luminosity and time-delay distributions, can be best used to determine more restrictive cosmological parameter constraints. In this study, we test the effect of adding 25 OzDES MgII RM QSOs as well as 25 lower-quality SDSS RM CIV QSOs, which increases the previous sample of RM QSOs by $\sim 36\%$. Although cosmological parameter constraints become tighter for some cosmological models after adding these new QSOs, the new combined data sets have increased differences between R-L parameter values obtained in different cosmological models and thus a lower standardizability for the larger MgII + CIV compilation. Different time-delay methodologies, particularly the ICCF and CREAM methods used for inferring time delays of SDSS RM QSOs, slightly affect cosmological and R-L relation parameter values, however, the effect is negligible for (smaller) compilations of robust time-delay detections. Our analysis indicates that increasing the sample size is not sufficient for tightening cosmological constraints and a quality cut is necessary to obtain a standardizable RM QSO sample.