Exploring the origin of moving groups and diagonal ridges by simulations of stellar orbits and birthplaces

TL;DR

This study uses simulations of stellar orbits within a Galactic potential to explain the origin of moving groups and diagonal ridges in the Milky Way, linking them to spiral-arm resonances and their long-term stability.

Contribution

It demonstrates that spiral-arm resonances can produce long-lived kinematic structures and links specific moving groups to their birthplaces and resonance origins.

Findings

Moving groups are associated with spiral-arm corotation resonance.

Hercules stream results from high-order inner Lindblad resonances.

Diagonal ridges are explained by spiral resonances in stellar velocity distributions.

Abstract

The present paper is the culminating one of a series aimed to contribute to the understanding of the kinematic structures of the solar neighbourhood (SN), explaining the origin of the Local Arm and relating the moving groups with the spiral-arms resonances in the disk. With a model for the Galactic potential, with the Sun inside the spiral corotation resonance (CR), we integrate the 2D orbits of test particles distributed in birthplaces along the main spiral arms, the Local Arm, and in the axisymmetric disk. A comparison of the resulting U-V plane of the SN with that provided by Gaia DR2 confirms our previous conclusion that the moving groups of Coma Berenices, Pleiades, and Hyades are associated with the CR, and that the Hercules stream is formed by the bulk of high-order inner Lindblad resonances. The kinematic structures result from stellar orbits trapped by the spiral resonances in a timespan of ~ 1 Gyr, indicating the long-living nature of the spiral structure and challenging recent arguments in favor of short-lived structures originated from incomplete phase mixing in the Galactic disk. As a byproduct, our simulations give some insight into the birthplaces of the stars presently located in the SN; the majority of stars of the main moving groups and the Hercules stream were likely born in the Local Arm, while stars of the Sirius group possibly originated from the outer segment of the Sagittarius-Carina arm. We also propose the spiral resonances as the dynamical origin for the diagonal ridges in the Galactic distribution of rotation velocities.