Kinematic and dynamics of the Milky Way

The new data of the Gaia mission of the European Space Agency is leading us into a new era of the study of the kinematics of our Galaxy. Gaia offers the position of each star in six-dimensional (6D) phase space: three dimensions of spatial information plus three dimensions of velocity. Gaia data provide accurate distance determination allowing to test the hypothesis of stationary equilibrium of the Milky Way. We have extended the kinematics maps of Gaia-DR2 data  in a range of heliocentric distances by a factor of two to three larger with respect to the official Gaia collaboration maps, out to R = 20 kpc, by applying a statistical deconvolution of the parallax errors based on the Lucy’s inversion. The newly extended maps provide substantial, new and corroborated information about the disk kinematics showing that the MilkyWay is far from a simple stationary configuration in rotational equilibrium, but it is characterized by streaming motions in all velocity components with conspicuous velocity gradients. We have checked that other galatic surveys (the Apache Point Galactic Evolution Experiment and the H I maps along the same line of sight) give a similar signal for what concerns the radial velocity only. We have then investigated the dynamical effects produced by different physical mechanisms that can explain the derived kinematic maps and we have compared the predictions of different dynamical models (i.e., Mond, CDM and deviations from the Jeans equilibrium) with the data of the Milky Way.