Evidence for the Hierarchical Formation of the Galactic Disk in the Solar Neighborhood

Yu-Fu Shen, Zhuohan Li

Published 2024-08-26Version 1

According to the hierarchical clustering scenario, galaxies like the Milky Way form hierarchically, and many supporting evidences have been found in the Galactic halo. However, most stars in the Milky Way are disk stars. Disk stars have almost lost their spatial distribution and kinematic features at birth, retaining solely chemical signatures. Identifying such substructures using abundances of iron or light elements is difficult due to their high degeneracy. Heavy elements, especially neutron capture elements have limited sources so have lower degeneracy, but spectral line fitting of these elements is tough, requiring mid to high resolution spectra, which are currently limited in sample size. This work utilizes the overall effect of changing in abundances to introduce the information of heavy elements, especially neutron capture elements to weaken the degeneracy of [Fe/H]. The analysis suggests the presence of at least 12 clusters, proves that the Galactic Disk form hierarchically. We excluded giants to prevent the possibly impact of mixing effects and that of too large differences in surface gravity, so the conclusions were all drawn from the solar neighborhood.