On the Migration Origin of the Hercules Moving Group with GAIA, LAMOST, APOGEE, and GALAH Surveys

TL;DR

This study uses Gaia DR3 and spectroscopic surveys to analyze the Hercules moving group, revealing its metallicity, age gradients, and likely origin as stars undergoing radial migration linked to Galactic bar resonances.

Contribution

It provides new insights into the substructure, metallicity, and age distributions of the Hercules moving group, suggesting a radial migration origin and association with Galactic bar resonances.

Findings

HMG is more metal-rich than the Galactic disk.

H2 is more metal-rich and older than H1.

HMG shows distinct radial metallicity and age gradients.

Abstract

Using Gaia DR3 data and the wavelet transformation technique, we study the substructures of the Hercules moving group (HMG): Hercules 1 (H1) and Hercules 2 (H2). Spectroscopic survey data from LAMOST, APOGEE, and GALAH are used to obtain metallicities and ages of stars belonging to the HMG. Our analysis leads to several key findings as follows: ($a$) the HMG is on average richer in metallicity than the Galactic disk, with H2 being metal richer than H1; ($b$) the HMG likely has a radial metallicity gradient distinct from that of the disk; ($c$) the HMG is on average older than the disk, with H2 being older than H1; ($d$) the HMG likely has a radial age gradient distinct from that of the disk; and ($e$) the metallicity and age distributions of the HMG depend mainly on the Galactic radius but show no dependence on the azimuthal velocity. Taken all together, we conclude that the HMG is composed primarily of stars undergoing radial migration. We suggest that the HMG is associated with a higher-order dynamical resonance of the bar of the Galaxy.