Kinematics & Chemistry of Halo Substructures: The Vicinity of the Virgo Over-Density

TL;DR

This study uses spectroscopic observations to analyze halo substructures near the Virgo Over-Density, revealing a tri-axial dark matter halo, a wider metallicity distribution in Sagittarius, and new stellar members.

Contribution

It provides new spectroscopic data and models that favor a tri-axial dark matter halo and uncovers more metal-poor Sagittarius members, expanding understanding of halo substructures.

Findings

Favours a tri-axial dark matter halo over prolate models.

Uncovers more metal-poor Sagittarius K-giant members.

Identifies five new carbon stars in the region.

Abstract

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 ([Fe/H] = -1.7 +/- 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.