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

Abstract

Context. Debris from past merger events is expected and also known, to some extent, to populate the stellar halo near the Sun. Aims. We aim to identify and characterise such merger debris using Gaia DR3 data supplemented with metallicity and chemical abundance data from LAMOST LRS and APOGEE for halo stars within 2.5 kpc from the Sun. Methods. We utilised a single linkage-based clustering algorithm to identify over-densities in the integrals of motion space that could be due to merger debris. Combined with metallicity information and chemical abundances, we characterised these statistically significant over-densities. Results. We find that the local stellar halo contains seven main dynamical groups, with some of them shown to be in situ and some of accreted origin, most of which are already known. We report the discovery of a new substructure, which we dubbed ED-1. In addition, we find evidence for 11 independent smaller clumps, 5 of which are new: ED-2, 3, 4, 5, and 6, and typically rather tight dynamically. We identify their narrow range of metallicities, along with their abundances when available, as well as their locations in the integrals of motion space, which are suggestive of an accreted origin. Conclusions. The local halo contains an important amount of substructure of both in situ and accreted origins.