# The moving groups as the origin of the vertical phase space spiral

## TL;DR

This study shows that the vertical phase space spiral observed near the Sun is caused by known moving groups, challenging the idea that external events or short-lived structures are responsible, and supports a longer formation timescale for these groups.

## Contribution

It demonstrates that the vertical phase space spiral is produced by moving groups without requiring external perturbations, suggesting a longer formation timescale for these groups.

## Key findings

- Vertical phase space spiral is caused by moving groups.
- No evidence of incomplete phase mixing in the vertical disk.
- Supports longer formation timescale (~a few Gyr) for moving groups.

## Abstract

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.