Redshift-evolutionary X-ray and UV luminosity relation of quasars from Gaussian copula

TL;DR

This study develops a redshift-evolutionary three-dimensional $L_X-L_{UV}$ relation for quasars using copula, demonstrating its superiority over standard models and confirming quasars as reliable cosmic distance indicators.

Contribution

It introduces a novel copula-based method to model the $L_X-L_{UV}$ relation with redshift evolution, improving the reliability of quasars for cosmology.

Findings

The copula-based $L_X-L_{UV}$ relation is more viable than the standard one.

Observations favor the redshift-evolutionary relation over 3 sigma.

The data strongly support the three-dimensional $L_X-L_{UV}$ relation.

Abstract

We construct a three-dimensional and redshift-evolutionary X-ray and ultraviolet ($L_X-L_{UV}$) luminosity relation for quasars from the powerful statistic tool called copula, and find that the constructed $L_X-L_{UV}$ relation from copula is more viable than the standard one and the observations favor the redshift-evolutionary relation more than $3\sigma$. The Akaike and Bayes information criterions indicate that the quasar data support strongly the three-dimensional $L_X-L_{UV}$ relation. Our results show that the quasars can be regarded as a reliable indicator of the cosmic distance if the $L_X-L_{UV}$ relation from copula is used to calibrate quasar data.