A strategy for astrometric quasar selection with Gaia DR3 and its application to discover new luminous $z>2$ quasars
Year: 2026
Type: preprint
Abstract: We aim to provide a cookbook for purely astrometric selection of quasars with Gaia DR3 and to provide an example of its use for the identification of very luminous $z>2$ quasars. We analyse the Gaia DR3 astrometry of confirmed quasars and stationary sources. We show that the proper motion signal to noise $μ/σ_μ$ follows a Rayleigh-like distribution. We also show the importance of properly taking into account the correlation between proper motions in right ascension and declination, as well as the non-linear error propagation. We adopt the Mahalanobis distance to the null proper-motion hypothesis. A scaled $χ^2$ distribution with $k=2$ and scale $s=1.1485$ is fitted to Gaia-CRF3; the corresponding $\pm2σ$ Gaussian-equivalent threshold is $D^2_{M(μ)}<7.097$. The final criteria combine this with the parallax condition and $\mathrm{ruwe}<1.4$. Applying the new criteria to the SDSS DR16Q confirmed quasars, the recovery rate is $90.25\%$. The suggested purely astrometric selection significantly improves both completeness and purity compared to other strategies used in the literature, reaching a quasar purity of approximately $95\%$ ($\sim2σ$ Gaussian-equivalent). It can be used to improve the selection purity and completeness for future quasar surveys. As an example, we use the suggested strategi to locate 24 very bright $z>2$ quasars without redshifts in the literature. Our proposed astrometric selection strategy recovers 95\% of known quasars. Its potential use for new discoveries is demonstrated by the identification of 24 very luminous $z>2$ quasars. Ten of these are new discoveries and for an additional seven we correct the redshifts determined by other methods.}
Source: arXiv (Cornell University)
Authors: Li, J., Fynbo, J. P. U.
Institution: University of Copenhagen
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Gordon and Betty Moore Foundation, Yale University, Carnegie Institution of Washington, Vanderbilt University, Ohio State University, California Institute of Technology, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, University of Portsmouth, New Mexico State University, European Space Agency, York University, University of Oxford, European Commission, Danmarks Grundforskningsfond, Chinese Academy of Sciences, Ministério da Ciência, Tecnologia e Inovação, Ministerio de Ciencia e Innovación, Universidad Nacional Autónoma de México, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, National Development and Reform Commission, Max-Planck-Institut für Astrophysik, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, Jet Propulsion Laboratory, University of Colorado Boulder, Science and Technology Facilities Council, Leibniz-Gemeinschaft, National Astronomical Observatories, Chinese Academy of Sciences, Division of Astronomical Sciences, Lawrence Berkeley National Laboratory
Awards: G1044631029, G1079818582, G1143651532, G1286236842, G1632040200, G1813527838, G1863003419, G271529020, G2824685711, G419881185, Cosmic Dawn Center (DAWN), G42916606, G4501827968, G498139845, G5004724115, G526230902, G6652958823, G6876926712, G7146827954, Management and Operations of the National Optical Astronomy Observatory, G7354628648
OpenAlex ID: W7221560345