Redshift-evolutionary X-Ray and UV Luminosity Relation of Quasars from Gaussian Copula

Abstract

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 3σ. 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.