GALAH DR4 halo substructures catalog

We recovered five kinematic structures in the action space with the wavelet transform. These groups are the Galactic disk, Splash, Gaia-Sausage-Enceladus (GSE), Thamnos1, and Thamnos2. We found that GSE has two peaks with the wavelet transform.

One of these peaks is located at SQRT(Jr)~=25kpc.km/s and is a result of contamination from disk stars. The other peak corresponds to the "cleanest" GSE population and is located above SQRT(Jr)~=40kpc.km/s. We also detected three peaks in Thamnos.

We linked two of them to Thamnos1, while the peak with the stars on the most retrograde orbits was linked to Thamnos2. The t-SNE algorithm confirmed these findings. We also analyzed individual elemental abundances of each group and found that Thamnos2 has a higher [alpha/Fe] ratio than the other groups and that iron-peak elements are more abundant in the Splash than in the halo groups, while the halo structures retain a higher r-process signature than the splashed disk.

A multiply peaked substructure we observe in action space in GSE and Thamnos suggests that the splashed disk extends beyond the borders of prograde orbits. Each of the four halo groups studied in this paper have unique chemodynamical properties that confirm their extra-galactic origin.