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gaia data release 3 documentation

14.1 Introduction

14.1.1 Completeness of source contents

The sources covered by the gaia_source table in Gaia DR3 and in Gaia EDR3 are the same, with identical astrometry. The source completeness is therefore unchanged.

  • Completeness has improved from Gaia DR2, as shown by several comparisons:

    • Comparison with OGLE (Section 14.4.1)

    • More stars in the centre of Andromeda and in M32 versus Gaia DR2 (Section 14.4)

    • Checks in crowded globular clusters (Section 14.7) show that the completeness is generally higher than in Gaia DR2, but strongly depending on the density. In dense areas of globular clusters, a percentage up to 20-30% of stars with astrometry do not have GBP and GRP magnitudes Open clusters are more favourable cases and in general the percentage of stars missing GBP, GRP is of the order of 1%-3%. Some artefacts on the completeness showing the effect of the scanning law are visible but the number is reduced in comparison to Gaia DR2.

    • Small gain in resolution due to the new criterion for duplicated sources (Section 14.2, Figure 14.1).

  • Bright stars environment is clean, no completeness problem found around bright stars (Section 14.2.1).

  • Based on star counts, the Gaia DR3 catalogue seems to be essentially complete between G=12 and G=17 (Section 14.3). Thus, the source list for the release will be incomplete at the bright end and has an ill-defined faint magnitude limit. Fainter than G=17 the completeness is complex, being affected by crowding and strongly depending on celestial position (Section 14.2). In any case, comparison with the GOG simulation shows that Gaia DR3 completeness has improved with respect to Gaia DR2 at G=19, although it is still not as high as expected (Section 14.3, Figure 14.39).

  • The combination of the Gaia scan law coverage and the filtering on data quality which was done prior to the publication of Gaia EDR3, can lead to some regions of the sky with source density fluctuations that reflect the scan law pattern. In addition, gaps may exist in the source distribution. This becomes more marked if one uses subsets of different astrometric solutions (2p, 5p, 6p).

  • In any case, no significant ‘holes’ are found in the sky (Section 14.2).

  • Comparisons to WDS show a high completeness for separation above 1′′, but a rapid decrease at smaller separations (Section 14.4).