2025MNRAS.542.2389H

This paper is devoted to some statistical analysis of more than 2 million quasars included in the recent Large Quasar Astrometric Catalogue (LQAC-6) compilation, whose a large proportion is subject to optimized astrometry, coming from the Gaia DR3 catalogue, published in 2022. The characterization of LQAC-6 objects not present in DR3 due to the cut-off of Gaia at $G=21$ is clearly shown. We also study the distribution of the equatorial and galactic coordinates, emphasizing the imbalance between the northern and southern hemispheres, and a dramatic depletion of objects at small galactic latitudes. Moreover we characterize the increase of the uncertainty both in position and in proper motion, with increasing magnitude. We check the quality of parallax values as given in DR3. We also compare the value of the redshifts as given by Gaia and ground based spectroscopy, showing a large disagreement for a significant ratio of the sample. We also investigate how very dense Active Galactic Nuclei catalogues, such as the AGN and Galaxy Evolution Survey, should ameliorate the sky coverage of the celestial reference frame. Finally, we clearly show how the absolute magnitude of quasars decreases as their redshift increases, and we demonstrate that for a given redshift, radio-loud quasars are significantly brighter, by around 2 mag, than radio-quiet ones.