New stellar velocity substructures from Gaia DR3 proper motions

TL;DR

This paper utilizes Gaia DR3 data to identify new and known stellar velocity substructures in the Milky Way, revealing insights into its dynamical history without relying solely on radial velocity measurements.

Contribution

It introduces a novel method to analyze full 3D stellar velocity distributions from Gaia data, discovering new stellar streams and confirming known merger remnants.

Findings

Detection of a new moving group MMH-0 in the disc.

Identification of prominent merger-related structures in the stellar halo.

Discovery of two new halo substructures, MMH-1 and MMH-2.

Abstract

Local stellar motions are expected, and have been shown, to include signatures of the Galaxy's past dynamical evolution. These are typically divided into the disc, which shows the dynamical effects of spiral arms and the bar, and the stellar halo, with structures thought to be debris from past mergers. We use Gaia Data Release 3 to select large samples of these populations without limiting them to sources with radial velocities. We apply a penalised maximum likelihood method to these samples to determine the full 3D velocity distribution in Cartesian $(U, V, W)$ or spherical $(v_r, v_\phi, v_\theta)$ coordinates. We find that the disc population is dominated by four moving groups and also detect a new moving group at $(U, V) = (-10, -15)$ km s$^{-1}$ which we call MMH-0. For the stellar halo, we isolate the accreted component with cuts in transverse velocity and the colour-magnitude diagram. In this component we find several known structures believed to be caused by past mergers, particularly one around $(v_r, v_\phi, v_\theta) = (-150, -300, -100)$ km s$^{-1}$ appears more prominent than previously claimed. Furthermore we also identify two new structures near $(v_r, v_\phi, v_\theta) = (225, 25, 325)$ km s$^{-1}$ and $(0, 150, -125)$ km s$^{-1}$ which we refer to as MMH-1 and MMH-2 respectively. These results give new insights into local stellar motions and shows the potential of using samples that are not limited to stars with measured line-of-sight velocities, which is key to providing large samples of stars, necessary for future studies.