The Gaia DR3 view of dynamical substructure in the stellar halo near the Sun

TL;DR

This study uses Gaia DR3 data combined with spectroscopic surveys to identify and characterize dynamical substructures in the local stellar halo, revealing known and new merger debris groups.

Contribution

It introduces a clustering approach in Integrals of Motion space to detect and analyze halo substructures, including the discovery of new debris groups.

Findings

Identified 7 main dynamical groups in the local halo.

Discovered a new substructure named ED-1.

Found 5 new smaller clumps with likely accreted origins.

Abstract

The debris from past merger events is expected and, to some extent, known to populate the stellar halo near the Sun. We aim to identify and characterise such merger debris using Gaia DR3 data supplemented by metallicity and chemical abundance information from LAMOST LRS and APOGEE for halo stars within 2.5 kpc from the Sun. We utilise a single linkage-based clustering algorithm to identify over-densities in Integrals of Motion space that could be due to merger debris. Combined with metallicity information and chemical abundances, we characterise these statistically significant over-densities. We find that the local stellar halo contains 7 main dynamical groups, some of in-situ and some of accreted origin, most of which are already known. We report the discovery of a new substructure, which we name ED-1. In addition, we find evidence for 11 independent smaller clumps, 5 of which are new: ED-2, 3, 4, 5 and 6 are typically rather tight dynamically, depict a small range of metallicities, and their abundances when available, as well as their location in Integrals of Motion space, suggest an accreted origin. The local halo contains an important amount of substructure, of both in-situ and accreted origin.