Probing the Astrometric Properties of Gaia EDR3 Quasars at the Faintest Magnitudes

Abstract

Gaia early data release 3 (EDR3) provides about 1.6 million QSO-like objects. Measuring the systematic residuals of the quasars convincingly in Gaia EDR3 is paramount for further fundamental astronomy use. We aim to conduct an independent assessment of the astrometric quality of Gaia EDR3 utilizing a sizable and confirmed extragalactic sources catalog. By positional cross-matching the known quasars to EDR3, we obtain a list of 299,004 confirmed QSOs. Together with the quasars identified in EDR3, we calculated the generalized moving mean of proper motions and parallaxes. Using spherical harmonics, the parallaxes and the proper motions are expanded to investigate their astrometric features. The global parallax bias is ∼−21 μas and ∼−27 μas for the five-parameter solution and the six-parameter solution samples, respectively. The mean proper motion of the five-parameter solution QSO-like subset is consistent with zero, while the mean proper motion of the six-parameter solution subset is a few μas yr−1 biased. The typical rotation and glide vector for the five-parameter solution quasars are (+3, +2, +1) ± 0.5 μas yr−1 and (0, −4, −2) ± 0.5 μas yr−1, respectively. Small systematic dependence of the rotation on the Gaia color and the G magnitude exists. The parallaxes of EDR3 quasars show an rms amplitude of 9.9 μas spatial correlation with the angular of ≥18°. At the level of Gaia EDR3's uncertainties, the quadrupole components of the vectorial spherical harmonics show that the mass-energy density of the gravitational waves ΩGW is about 0.0073 h −2.