Characterizing the astrometric quality of AGNs in Gaia-CRF3

TL;DR

This paper evaluates the astrometric accuracy of AGNs in Gaia-CRF3, identifying sources of systematic errors, and introduces a quality index to select reliable AGNs for celestial reference frames.

Contribution

It provides a detailed analysis of Gaia DR3 AGN astrometry and proposes a new quality metric to improve reference frame accuracy.

Findings

Significant astrometric offsets are caused by dual or lensed quasars.

The quality index correlates strongly with astrometric errors.

The index effectively identifies high-fidelity AGNs for reference frames.

Abstract

Active Galactic Nuclei (AGNs), owing to their great distances and compact sizes, serve as fundamental anchors for defining the celestial reference frame. With about 1.9 million AGNs observed in Gaia DR3 at optical precision comparable to radio wavelengths, Gaia provides a solid foundation for constructing the next-generation, kinematically non-rotating optical reference frame. Accurate assessment of systematic residuals in AGN astrometry is therefore crucial. In this talk, we analysed the parallaxes and proper motions of Gaia DR3 AGNs to characterize systematic errors and their correlations with various physical and observational properties. A subset of Gaia-CRF3 AGNs exhibits significant astrometric offsets, mainly arising from dual or lensed quasars whose structural variations induce photocenter jitter, mimicking parallax and proper motion. Such sources must be carefully excluded from reference frame construction. To this end, we introduce an astrometric quality index for each source to quantify its astrometric reliability. The results reveal a strong correlation between lower quality index values and increasing errors in position, proper motion, and parallax, demonstrating that the proposed index provides an effective metric for selecting high-fidelity AGNs as primary reference sources.