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 MG and GRP. 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.
