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In this study we use a sample of about 9 million SkyMapper stars withmetallicities to investigate the properties of the two stellar populations seenin the high-velocity ($V_{\rm T} > 200$ km/s) Gaia DR2 Hertzsprung-Russelldiagram. Based on 10,000 red giant branch (RGB) stars (out of 75,000 with highvelocity), we find that the two sequences have different metallicitydistribution functions; one peaks at $-1.4$ dex (blue sequence) and the otherat $-0.7$ dex (red sequence). Isochrones with ages in the range $11$-$13.5$Gyr, and metallicities chosen to match the observations for each sequence, fitthe turnoffs and broad RGBs well, indicating that the two populations formed atcomparable times within the uncertainties. We find that the mean tangentialvelocity of disk stars increases steadily with decreasing metallicity, and thatthe red sequence is made up of the high-velocity stars at the lowestmetallicities of the thick-disk population. Using relative number densities, wefurther find that the red-sequence stars are more centrally concentrated in theGalaxy, and we estimate the radial scale length of this population to be on theorder of $2$-$3$ kpc. The blue-sequence stars, on the other hand, follow anearly flat radial density profile. These findings tighten the link between thered-sequence stars and the chemically defined thick disk.

Characteristics of the two sequences seen in the high-velocity Hertzsprung-Russell diagram in Gaia DR2