Stellar Kinematic Constraints on Galactic Structure Models Revisited: Bar and Spiral Arm Resonances

TL;DR

This study explores how spiral arms and the Galactic bar influence stellar kinematics in the Milky Way, revealing that spiral arms can significantly shape local stellar groups and dark matter structures, challenging previous assumptions.

Contribution

It demonstrates that spiral arm resonances can create observable stellar kinematic groups, offering a new perspective on Galactic structure modeling.

Findings

Spiral arms can be as influential as the Galactic bar in shaping stellar kinematics.

Kinematic groups like Hercules and Arcturus can originate from spiral arm resonances.

Dark matter disk structures are affected by the same resonances, independent of galaxy formation history.

Abstract

We study the phase space available to the local stellar distribution using a Galactic potential consistent with several recent observational constraints. We find that the induced phase space structure has several observable consequences. The spiral arm contribution to the kinematic structure in the solar neighborhood may be as important as the one produced by the Galactic bar. We suggest that some of the stellar kinematic groups in the solar neighborhood, like the Hercules structure and the kinematic branches, can be created by the dynamical resonances of self-gravitating spiral arms and not exclusively by the Galactic bar. A structure coincident with the Arcturus kinematic group is developed when a hot stellar disk population is considered, which introduces a new perspective on the interpretation of its extragalactic origin. A bar-related resonant mechanism can modify this kinematic structure.We show that particles in the dark matter disk-like structure predicted by recent LCDM galaxy formation experiments, with similar kinematics to the thick disk, are affected by the same resonances, developing phase space structures or dark kinematic groups that are independent of the Galaxy assembly history and substructure abundance. We discuss the possibility of using the stellar phase space groups as constraints to non-axisymmetric models of the Milky Way structure.