Gaia Data Release 2: The Celestial reference frame (Gaia-CRF2)

Understand

The second release of Gaia data (Gaia DR2) contains the astrometric parameters for more than half a million quasars.

• This set defines a kinematically non-rotating reference frame in the optical domain referred to as the Gaia-CRF2.
• The Gaia-CRF2 is the first realisation of a non-rotating global optical reference frame that meets the ICRS prescriptions, meaning that it is built only on extragalactic sources.
• It consists of the positions of a sample of 556 869 sources in Gaia DR2, obtained from a positional cross-match with the ICRF3-prototype and AllWISE AGN catalogues.