Current and future applications of Reverberation-mapped quasars in Cosmology

TL;DR

Reverberation mapping of quasars, especially using MgII lines at higher redshifts, offers a promising method for cosmological measurements, with recent corrections improving the accuracy of the Radius-Luminosity relation and potential for large-scale surveys like LSST.

Contribution

This paper presents new MgII reverberation mapping results at high redshift, introduces corrections for highly accreting sources, and discusses the application of these methods to future cosmological studies with LSST.

Findings

RL relation holds for MgII at high redshift within uncertainties

Correction for highly accreting sources reduces scatter in RL relation

Cosmological parameters can be constrained within 2σ using reverberation mapping data

Abstract

Reverberation mapping technique is an important milestone in AGN demographics, kinematics and the structure of the Broad Line Region (BLR) based on the time-delay response between the continuum and emission line. The time delay is directly related to the size of BLR which is related to the continuum luminosity of the source, producing the well-known Radius-Luminosity (RL) relation. The majority of sources have been monitored for their H$\beta$ emission line in low redshift sources ($z<0.1$), while there are some attempts using the MgII line for higher redshifts. We present a recent MgII monitoring for the quasar CTS C30.10 ($z=0.90$) observed with the 10-meter SALT, for which RL scaling based on MgII holds within measurement and time-delay uncertainties. One of the most important advantages of reverberation mapping technique is the independent determination to the distant source, and considering the large range of redshifts and luminosities found in AGNs, their application to cosmology is promising. However, recently it has been found that highly accreting sources show the time delays shorter than expected from RL relation. We propose correction for this effect using a sample of 117 H$\beta$ reverberating-mapped AGNs with $0.02<z<0.9$, recovering the low scatter along with the relation. We are able to determine the cosmological constants, $\Omega_m$ and $\Omega_\Lambda$ within 2$\sigma$ confidence level. We present the first steps in modelling of light curves for H$\beta$ and MgII and discuss the quasar selection in the context of photometric reverberation mapping with Large Synoptic Survey Telescope (LSST). With the onset of the LSST era, we expect a huge rise in the overall quasar counts and redshift range covered ($z\lesssim 7.0$), which will provide a better constraint of AGN properties with cosmological purposes.