Exploration of Halo Substructures in IoM Space with \textit{Gaia} DR3

TL;DR

This study uses Gaia DR3 data and clustering algorithms to identify known and new substructures in the Milky Way's stellar halo, revealing insights into their origins and properties.

Contribution

The paper introduces a novel application of HDBSCAN clustering in IoM space to discover and analyze both known and new stellar halo substructures using Gaia DR3 data.

Findings

Identified 5 known substructures including GSE, Helmi Streams, Sequoia, and Hot Thick Disc.

Discovered three new substructures: PG1, PG2, and the Low Energy Group.

Suggested possible origins for new substructures based on their kinematic and metallicity properties.

Abstract

Using kinematic data from the Gaia Data Release 3 catalog, along with metallicity estimates robustly derived from Gaia XP spectra, we have explored the Galactic stellar halo in search of both known and potentially new substructures. By applying the HDBSCAN clustering algorithm in IoM space (i.e. $E,L_{z}$ and $L_{\perp}$$ = \sqrt{L_{x}^2+L_{y}^2}$), we identified 5 previously known substructures: Gaia-Sausage-Enceladus (GSE), Helmi Streams, I'itoi + Sequoia and Hot Thick Disc. We additionally found NGC 3201 and NGC 5139 in this work, and NGC 3201 shares similar distributions in phase space and metallicties to Arjuna, which possibly implies that they have the same origin. Three newly discovered substructures are Prograde Substructure 1 (PG1), Prograde Substructure 2 (PG2) and the Low Energy Group. PG1, with a higher $V_{\phi}$ than typical GSE member stars, is considered as either a low eccentricity and metal-rich part of GSE or part of the metal-poor disc. PG2, sharing kinematic similarities with Aleph, is thought to be its relatively highly eccentric component or the mixture of Aleph and disc. The Low Energy Group, whose metal-poor component of metallicity distribution function has a mean value [M/H] $\sim$ $-$1.29 (compared to that of Heracles [M/H] $\sim$ $-$1.26), may have associations with Heracles.