The moving groups as the origin of the vertical phase space spiral
  Using the Gaia data release 2 (DR2), we analyzed the distribution of stars in
the close vicinity of the Sun in the full 3D position-velocity space. We have
found no evidence of incomplete phase mixing in the vertical direction of the
disk, which could be originated by some external events. We show that the
vertical phase space spiral $Z$-$V_z$ is produced by the well-known moving
groups (MGs), mainly by Coma-Berenices, Pleiades-Hyades and Sirius, when the
statistical characteristics (mean, median, or mode) of the azimuthal velocity
$V_\varphi$ are used to analyze the distribution in the vertical
position-velocity plane. This result does not invoke external perturbations and
is independent on the internal dynamical mechanisms that originate the MGs. Our
conclusions counterbalance current arguments in favor of short-lived (between
300 and 900 Myr) structures in the solar neighborhood. Contrarily, they support
the hypothesis of a longer formation time scale (around a few Gyr) for the MGs.
