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gaia data release 3 documentation

14.3 Comparison to models

14.3.3 Proper motions

The projections of the proper motion along the Galactic coordinates, μl and μb, are computed in order to see systematics due to the Galactic rotation. The median of the proper motions is computed in each HEALPix pixel and shown in Figure 14.42.

Figure 14.42: Median of proper motions μl (top panels) and μb (lower panels) inmasyr-1 in Gaia DR3 (left), in GOG20 (middle), and their absolute differences (right) in mas/yr in HEALPix pixels, in the magnitude range 17<G<18.

The model and data present approximately similar patterns in all magnitude ranges. However, there are systematics, as was already noted in the validation of Gaia DR2. It is most probable that these systematic differences are due to inaccuracy in modelling (e.g. the Galactic rotation).

Figure 14.43 gives the proper motion averaged over the whole sky per magnitude bin, for Gaia DR3, Gaia DR2, and GOG20. At bright magnitudes, the difference between Gaia DR3 and GOG20 in μl is at the level of 0.05masyr-1, and increases at fainter magnitudes (up to 0.4masyr-1). The systematics are less than 0.05masyr-1 in μb.

Figure 14.43: Median of proper motions inmasyr-1 over the whole sky as a function of magnitude (left: μl, right: μb) in Gaia DR3 (blue) and Gaia DR2 (pink), compared to GOG20 (green).

Summary of the results:

  • The Gaia DR3 data are as expected from our knowledge of the Galactic kinematics up to very faint magnitudes and it is probably the model which suffers from systematics, or does not account for asymmetries. Indeed we note that the change of kinematics from GOG18 to GOG20 globally allows for a better agreement with the data.