Two substructures in the nearby stellar halo found in Gaia and RAVE

TL;DR

This study identifies two new substructures in the nearby stellar halo using Gaia DR2 and RAVE data, revealing details about their energy, angular momentum, and possible origins as dwarf galaxy debris.

Contribution

The paper introduces the discovery of two previously unknown stellar halo substructures using combined Gaia and RAVE data, with detailed analysis of their properties.

Findings

Two significant substructures, GR-1 and GR-2, identified in the stellar halo.

GR-1 has high binding energy and small z-angular momentum.

GR-2 is metal-rich and retrograde.

Abstract

We use the second Gaia data release (Gaia DR2), combined with RAVE spectroscopic surveys, to identify the substructures in the nearby stellar halo. We select 3,845 halo stars kinematically and chemically, and determine their density distribution in energy and angular momentum space. To select the substructures from overdensities, we reshuffle the velocities and estimate their significance. Two statistically significant substructures, GR-1 and GR-2, are identified. GR-1 has a high binding energy and small $z$-angular momentum. GR-2 is metal-rich but retrograde. They are both new substructure, and may be accretion debris of dwarf galaxies.