Vertical kinematics of the thick disc at 4.5 < R < 9.5 kpc

Abstract

We explored a method to reconstruct the distribution function of the Galactic thick disc within the action space where nearby thick-disc stars are distributed. By applying this method to 127 chemically-selected thick-disc stars in the Solar neighbourhood, we found that the vertical velocity dispersion that corresponds to the reconstructed distribution function declines approximately as $\exp (-R/R_s)$ at 4.5 kpc < R < 9.5 kpc, with $R_s$ = 8.3 $\pm$ 1.1 (rand.) $\pm$ 1.6 (sys.) kpc. Also, we found that the vertical velocity dispersion $\sigma_z$ of our local thick-disc stars shows only weak dependency on radial and azimuthal velocities $(v_R, v_\phi)$. We discuss possible implications of these results on the global structure of the Milky Way thick disc.