A catalog of 551,214 low-mass, metal-poor stars in the Local Galactic halo from Gaia EDR3

We present a census of the population of local (d < 2 kpc) Galactic halo stars, based on a search of stars with large proper motions (> 40 mas/yr) from the Gaia Early Data Release 3. From this we assemble a catalog of 551,214 low-mass halo stars, for which we also derive photometric metallicity estimates. We assembled 17,803 stars as a metallicity calibration subset from various large spectroscopic surveys, such as SDSS SEGUE/APOGEE, GALAH, LAMOST, and from Hejazi et al. (2020). We expand on these results to construct a color-magnitude-metallicity grid, which can be used to estimate metallicities for all the stars using their values of M_G and G_RP. We find that stars in our catalog share similar kinematics as reported in recent studies of more luminous Galactic halo stars. Our sample notably shows likely new members of Gaia-Enceladus Stream of which mean photometric metallicity estimate is around -1.2 dex. We further explore how the velocity-space distribution of low-mass M stars varies with metallicity, and tentatively identify possible chemically distinct sub-populations, which could potentially be revealed in greater detail with radial velocity measurements the full Gaia Data Release 3 and from large spectroscopic surveys like SDSS-V, DESI MW survey, WEAVE, and/or 4MOST.