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We have developed a chemo-dynamical approach to assign 36,010 metal-poorSkyMapper stars to various Galactic stellar populations. Using two independenttechniques (velocity and action space behavior), $Gaia$ EDR3 astrometry, andphotometric metallicities, we selected stars with the characteristics of the"metal-weak" thick disk population by minimizing contamination by the canonicalthick disk or other Galactic structures. This sample comprises 7,127 stars,spans a metallicity range of $-3.50<${\metal}~$<-0.8$, and has a systematicrotational velocity of $\langle V_\phi\rangle=154$\,km\,s$^{-1}$ that lags thatof the thick disk. Orbital eccentricities have intermediate values betweentypical thick disk and halo values. The scale length is$h_{R}=2.48^{+0.05}_{-0.05}$\,kpc and the scale height is$h_{Z}=1.68^{+0.19}_{-0.15}$\,kpc. The metallicity distribution function iswell fit by an exponential with a slope of $\Delta\log{\rmN}/\Delta\metal=1.13\pm0.06$. Overall, we find a significant metal-poorcomponent consisting of 261 SkyMapper stars with \metal$<-2.0$. While oursample contains only eleven stars with {\metal}~$\lesssim-3.0$, investigatingthe JINAbase compilation of metal-poor stars reveals another 18 such stars(five have {\metal}$<-4.0$) that kinematically belong to our sample. Thesedistinct spatial, kinematic and chemical characteristics strongly suggest thismetal-poor, phase-mixed kinematic sample to represent an independent diskcomponent with an accretion origin in which a massive dwarf galaxy radiallyplunged into the early Galactic disk. Going forward, we propose to call themetal-weak thick disk population as the Atari disk, given its likely accretionorigin, and in reference to it sharing space with the Galactic thin and thickdisks.

The Atari Disk, a Metal-Poor Stellar Population in the Disk System of the Milky Way