Stars in the Local Galactic Thick Disk and Halo in Gaia EDR3: A catalogue of Half a Million Local Main-sequence Stars with Photometric Metallicities

TL;DR

This paper presents a catalogue of over half a million local main-sequence stars in the Galactic thick disk and halo, derived from Gaia EDR3 data, with photometric metallicities calibrated from spectroscopic surveys, aiding future kinematic and chemical studies.

Contribution

The study introduces a large, calibrated catalogue of low-mass, high-velocity stars with photometric metallicities, enabling detailed analysis of Galactic halo structures without requiring radial velocities.

Findings

Recovered main local halo structures like Gaia-Enceladus and Helmi streams.

Found that low-mass, high-velocity stars share kinematic properties with luminous halo stars.

Catalogue serves as a target list for future spectroscopic surveys.

Abstract

We present a catalogue of 551,214 main-sequence stars in the local ($d < 2$ kpc) Galactic thick disk and halo, based on a search of stars with large proper motions ($\mu_{\mathrm{tot}} > 40.0$ mas/yr) in the Gaia Early Data Release 3. We derive photometric metallicity calibrated from the colour-luminosity-metallicity distribution of 20,047 stars with spectroscopic metallicities, collected from various spectroscopic surveys, including SDSS SEGUE/APOGEE, GALAH DR3, and LAMOST DR6. We combine these results to construct an empirical colour-magnitude-metallicity grid, which can be used to estimate photometric metallicities for low-mass metal-poor stars of K and M subtypes from their absolute $G$ magnitude and colour values. We find that low-mass, high-velocity stars in our catalogue share similar kinematics as reported in recent studies of more luminous Galactic halo stars. The pseudo-kinematic analysis of our sample recovers the main local halo structures, including the Gaia-Enceladus Stream and the Helmi stream; aside from these the local halo stars appear to show a remarkably smooth distribution in velocity space. Since the future Gaia data release will provide radial velocity measurements for only a small number of our sample, our catalogue provides targets of high interest for the future spectroscopic observation programs like SDSS-V, DESI MW survey, WEAVE, and/or 4MOST.