We present observations obtained with the AAT ’ s 2dF wide field spectrograph AAOmega of K-type stars located within a region of the sky which contains the Virgo Over-Density and the leading arm of the Sagittarius Stream .
On the basis of the resulting velocity histogram we isolate halo substructures in these overlapping regions including Sagittarius and previously discovered Virgo groups .
Through comparisons with N -body models of the Galaxy-Sagittarius interaction , we find a tri-axial dark matter halo is favoured and we exclude a prolate shape .
This result is contradictory with other observations along the Sagittarius leading arm , which typically favour prolate models .
We have also uncovered K-giant members of Sagittarius that are notably more metal poor ( \langle [ Fe/H ] \rangle = -1.7 \pm 0.3 dex ) than previous studies .
This suggests a significantly wider metallicity distribution exists in the Sagittarius Stream than formerly considered .
We also present data on five carbon stars which were discovered in our sample .