# 8.1 Introduction

Author(s): Xavier Luri, Claus Fabricius

This section summarises the results of the validation tests run by the Coordination Unit 9 (CU9) of DPAC on the Gaia EDR3 data. In several cases the issues found by these tests were repaired by reprocessing before the data release; these cases are not discussed here, since they are not of relevance for the published data. For the remaining cases we document the issue and in some cases give recommendations to mitigate them. We also encourage reading the release paper Fabricius et al. (2021). This paper provides a more concise overview of the validation findings as well as practical recommendations for the usage of the Gaia EDR3 data.

Please note that the CU9 validation was applied only to the astrometric (AGIS 3.2), Photometric (PhotPipe 3.3) and Radial Velocity data (from Gaia DR2) contained in the main GaiaSource table. Gaia EDR3 also contains some additional tables that have been produced and self-validated by other CUs:

• Simulated data from CU2: the GUMS universe model simulation and the GOG catalogue simulation

• Reference frame sources (FrameRotator table)

• AGN cross-id table

• Commanded scan law table

• Gaia DR2 to Gaia EDR3 match table

• Cross-matches with external catalogues

Globally, Gaia EDR3 is a significant improvement with respect to Gaia DR2:

• The parallax improvement is typically 20%

• The proper motions are typically a factor of 2 better

• Astrometry systematics have been reduced (including the parallax zero-point that is now estimated to be about $-20\mu$as)

• Photometry precision has significantly improved