Gaia Early Data Release 3. The celestial reference frame (Gaia-CRF3)

, S. A. Klioner, L. Lindegren, F. Mignard, J. Hernández, M. Ramos-Lerate, U. Bastian, M. Biermann, A. Bombrun, A. de Torres, E. Gerlach, R. Geyer, T. Hilger, D. Hobbs, U. L. Lammers, P. J. McMillan, H. Steidelmüller, D. Teyssier, C. M. Raiteri, S. Bartolomé, M. Bernet, J. Castañeda, M. Clotet, M. Davidson, C. Fabricius, N. Garralda Torres, J. J. González-Vidal, J. Portell, N. Rowell, F. Torra, J. Torra, A. G. A. Brown, A. Vallenari, T. Prusti, J. H. J. de Bruijne, F. Arenou, C. Babusiaux, O. L. Creevey, C. Ducourant, D. W. Evans, L. Eyer, R. Guerra, A. Hutton, C. Jordi, X. Luri, C. Panem, D. Pourbaix, S. Randich, P. Sartoretti, J. Alves, T. Lebzelter

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue.
Aims: We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality.
Methods: Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3).
Results: Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 µas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution.

Department of Astrophysics
External organisation(s)
Technische Universität Dresden, Lund University, Université Côte d'Azur, European Space Astronomy Centre (ESA), Scientific Software Center, Telespazio Vega UK Ltd., INAF-Osservatorio Astrofisico di Torino, Universitat de Barcelona, University of Edinburgh, ATG Europe for ESA/ESAC, Madrid, Spain, Leiden University, Osservatorio Astronomico, Science and Operations Department - Science Division (SCI-SC), Paris Observatory, University of Grenoble Alpes, Université Bordeaux, University of Cambridge, Université de Genève, Aurora Technology, Spain, Centre national d'études spatiales (CNES), Université Libre de Bruxelles, INAF - Osservatorio Astrofisico di Arcetri
Astronomy and Astrophysics
No. of pages
Publication date
Peer reviewed
Austrian Fields of Science 2012
103003 Astronomy, 103004 Astrophysics
ASJC Scopus subject areas
Astronomy and Astrophysics, Space and Planetary Science
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