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Photometric stellar surveys now cover a large fraction of the sky, probe tofainter magnitudes than large-scale spectroscopic studies, and are relativelyfree from the target-selection biases often associated with such studies.Photometric-metallicity estimates that include narrow/medium-band filters canachieve comparable accuracy and precision to existing low- andmedium-resolution spectroscopic surveys such as SDSS/SEGUE and LAMOST, withmetallicities as low as [Fe/H] $\sim -3.5$ to $-4.0$. Here we report on aneffort to identify likely members of the Galactic disk system among the VeryMetal-Poor (VMP; [Fe/H] $\leq$ -2) and Extremely Metal-Poor (EMP; [Fe/H] $\leq$-3) stars. Our analysis is based on a sample of some 11.5 million stars withfull space motions selected from the SkyMapper Southern Survey (SMSS) andStellar Abundance and Galactic Evolution Survey (SAGES). After applying anumber of quality cuts, designed to obtain the best available metallicity anddynamical estimates, we analyze a total of about 7.74 million stars in thecombined SMSS/SAGES sample. We employ two techniques which, depending on themethod, identify between 5,878 and 7,600 VMP stars (19% to 25% of all VMPstars) and between 345 and 399 EMP stars (35% to 40% of all EMP stars) thatappear to be members of the Galactic disk system on highly prograde orbits(v$_{\phi} > 150$ kms$^{-1}$), the majority of which have low orbitaleccentricities (ecc $\le 0.4$). The large fractions of VMP/EMP stars that areassociated with the MW disk system strongly suggests the presence of an earlyforming ``primordial" disk.

Candidate Members of the VMP/EMP Disk System of the Galaxy from the SkyMapper and SAGES Surveys