Standardizing a larger, higher-quality, homogeneous sample of reverberation-mapped H$\beta$ active galactic nuclei using the broad-line region radius-luminosity relation

TL;DR

This paper presents a significantly larger, high-quality sample of reverberation-mapped Hβ active galactic nuclei, demonstrating their potential for cosmological measurements and revealing a flatter radius-luminosity relation than previously observed.

Contribution

It provides the largest homogeneous Hβ RM AGN sample to date and analyzes its cosmological and physical properties, including the R-L relation slope and Eddington ratio dependence.

Findings

Sample size increased by a factor of 3.8 compared to previous data.

The R-L relation slope is flatter than expected from simple models.

Hβ R-L relation shows mild dependence on Eddington ratio.

Abstract

We present a high-quality, homogeneous sample of 157 H$\beta$ reverberation-mapped active galactic nuclei (RM AGNs) spanning redshifts $0.00308 \leq z \leq 0.8429$, which is approximately 3.8 times larger than the previously available high-quality homogeneous sample. Using the broad-line region radius$-$luminosity relation ($R-L$), which involves the broad H$\beta$ line time delay and the monochromatic luminosity at 5100\,\AA\,, we show that the sample is standardizable by using six spatially flat and nonflat cosmological models. The inferred cosmological model parameters are consistent within 2$\sigma$ uncertainties with those from better established baryon acoustic oscillation and Hubble parameter measurements, with the exception of two nonflat models that are ruled out by other data. The $R-L$ relation slope is found to be flatter ($\gamma=0.428 \pm 0.025$ in the flat $\Lambda$CDM model) than the slope expected from a simple photoionization model as well as the slope found previously for the smaller homogeneous sample. In addition, we find a mild dependence of H$\beta$ $R-L$ relation parameters as well as its intrinsic scatter on the Eddington ratio by comparing the $R-L$ relations for low- and high-accreting equal-sized subsamples. A future analysis of a larger homogeneous sample containing a broader range of luminosities and Eddington ratios is necessary to confirm the standardizability of H$\beta$ AGNs.