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We present deep CMDs for two Subaru Suprime-Cam fields in the Virgo StellarStream(VSS)/Virgo Overdensity(VOD) and compare them to a field centred on thehighest concentration of Sagittarius (Sgr) Tidal Stream stars in the leadingarm, Branch A of the bifurcation. A prominent population of MS stars isdetected in all three fields and can be traced as faint as g~24 mag. Usingtheoretical isochrone fitting we derive an age of 9.1(+1.0;-1.1)Gyr, a medianabundance of [Fe/H]=-0.70 (+0.15; -0.20)dex and d_helio of 30.9+-3.0kpc for theMS of the Sgr Stream Branch A. The dominant main sequence populations in thetwo VSS/VOD fields (Lsun ~265 deg, Bsun ~13 deg) are located at a mean distanceof 23.3+-1.6kpc and have an age ~8.2Gyr and an abundance[Fe/H]=-0.67(+0.16;-0.12)dex similar to the Sgr Stream stars. These parametersare also in good agreement with the age of the main population in theSagittarius dwarf (8.0+-1.5Gyr). They also agree with the peak in themetallicity distribution of 2-3Gyr old M-giants, [Fe/H] ~ -0.6dex, in the Sgrleading arm north. We then compare the results from the VSS/VOD fields with theSgr Tidal Stream model by Law & Majewski based on a triaxial Galactic halo thatis calibrated with SDSS Sgr A-branch and 2MASS M-giant stars. We find that themost prominent feature in the CMDs, the MS population at 23kpc, is notexplained by the model. Instead the model predicts in these directions a lowdensity filamentary structure of Sgr debris stars at ~9kpc and a slightlyhigher concentration of Sgr stars spread from 42-53kpc. At best there is onlymarginal evidence for the presence of these populations in our data. Ourfindings then suggest that while there are probably some Sgr debris starspresent, the dominant stellar population in the VOD originates from a differenthalo structure that has almost identical age and metallicity as some sectionsof the Sgr tidal stream.

Main Sequence Star Populations in the Virgo Overdensity Region