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gaia early data release 3 documentation

7.3 Comparison to models

7.3.2 Parallax distribution

The median of the parallax is computed in each healpix bin and presented in Figure 7.11 in three magnitude bins. The median parallaxes are generally in very good agreement between Gaia EDR3 and GOG20. There are however a few places where the difference is significant, close to the Galactic centre or the Galactic plane (in particular at intermediate magnitudes). The Magellanic Clouds also appear since they are not generated by the model and what we see is the difference between the median parallax in the Magellanic Clouds (of the order of 0.02 mas) and the median parallax of field stars in the same region (which depends on magnitude, see Figure 7.12).

Figure 7.11: Median of parallaxes in Gaia EDR3 (left), in GOG20 (middle) and their absolute differences (right) in mas, in 3 magnitude ranges 8<G<9 (top), 12<G<13 (middle), and 17<G<18 (bottom).

Figure 7.12 shows the parallax averaged over the whole sky per magnitude bin, for Gaia EDR3, Gaia DR2, and GOG20. There is a systematic difference which, in absolute value, depends on magnitude, and is quite high at bright magnitudes, more than 1 mas. This systematic is a bit reduced compared to Gaia DR2. At G>10 the difference goes below 0.1 mas.

Figure 7.12: Parallaxes in mas averaged over the whole sky as a function of magnitude for Gaia EDR3, GOG20, and Gaia DR2.

Summary of the results:

  • The median parallaxes are generally in very good agreement between Gaia EDR3 and the model.

  • There is a systematic difference which is quite high at bright magnitudes, but is reduced compared to Gaia DR2.