We present deep color-magnitude diagrams for two Subaru Suprime-Cam fields in the Virgo Stellar Stream ( VSS ) /Virgo Overdensity ( VOD ) and compare them to a field centred on the highest concentration of Sagittarius ( Sgr ) Tidal Stream stars in the leading arm , Branch A of the bifurcation .
A prominent population of main sequence stars is detected in all three fields and can be traced as faint as g \approx 24 mag .
Using theoretical isochrone fitting we derive an age of 9.1 ^ { +1.0 } _ { -1.1 } Gyr , a median abundance of [ Fe/H ] = -0.70 ^ { +0.15 } _ { -0.20 } dex and a heliocentric distance of 30.9 \pm 3.0 kpc for the main sequence of the Sgr Stream Branch A .
The dominant main sequence populations in the two VSS/VOD fields ( \Lambda _ { \sun } \approx 265 ^ { \circ } , B _ { \sun } \approx 13 ^ { \circ } ) are located at a mean distance of 23.3 \pm 1.6 kpc and have an age \sim 8.2 Gyr and an abundance [ Fe/H ] = -0.67 ^ { +0.16 } _ { -0.12 } dex similar to the Sgr Stream stars .
These statistically robust parameters , derived from photometry of 260 main sequence stars , are also in good agreement with the age of the main population in the Sagittarius dwarf galaxy ( 8.0 \pm 1.5 Gyr ) .
They also agree with the peak in the metallicity distribution of 2 - 3 Gyr old M-giants , [ Fe/H ] \approx - 0.6 dex , in the Sgr leading arm north .
We then compare the results from the VSS/VOD fields with the Sgr Tidal Stream model by Law & Majewski based on a triaxial Galactic halo shape that is empirically calibrated with SDSS Sgr A-branch and 2MASS M giant stars .
We find that the most prominent feature in the CMDs , the main sequence population at 23 kpc , is not explained by the model .
Instead the model predicts in these directions a low density filamentary structure of Sgr debris stars at \sim 9 kpc and a slightly higher concentration of Sgr stars spread over a heliocentric distance range of 42 - 53 kpc .
At best there is only marginal evidence for the presence of these populations in our data .
Our findings then suggest that while there are probably some Sgr debris stars present , the dominant stellar population in the Virgo Overdensity originates from a different halo structure that has almost identical age and metallicity as some sections of the Sgr tidal stream .