Stellar Over-densities in the Outer Halo of the Milky Way

Abstract

This study presents a tomographic survey of a subset of the outer halo (10-40 kpc) drawn from the Sloan Digital Sky Survey Data Release 6. Halo substructure on spatial scales of $>3$ degrees is revealed as an excess in the local density of sub-giant stars. With an appropriate assumption of a model stellar isochrone it is possible for us to then derive distances to the sub-giant population. We describe three new candidate halo substructures; the 160- and 180-degree over-densities (at distances of 17 and 19 kpc respectively and radii of 1.3 and 1.5 kpc respectively) and an extended feature at 28 kpc that covers at least 162 square degrees, the Virgo Equatorial Stream. In addition, we recover the Sagittarius dwarf galaxy (Sgr) leading arm material and the Virgo Over-density. The derived distances, together with the number of sub-giant stars associated with each substructure, enables us to derive the integrated luminosity for the features. The tenuous, low surface brightness of the features strongly suggests an origin from the tidal disruption of an accreted galaxy or galaxies. Given the dominance of the tidal debris of Sgr in this region of the sky we investigate if our observations can be accommodated by tidal disruption models for Sgr. The clear discordance between observations and model predictions for known Sgr features means it is difficult to tell unambiguously if the new substructures are related to Sgr or not. Radial velocities in the stellar over-densities will be critical in establishing their origins.

14 pages, 7 figures, PASA accepted

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Cited by in corpus (8)

• The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky Way Halo
• La Silla QUEST RR Lyrae Star Survey: Region I
• The Northern wraps of the Sagittarius Stream as traced by Red Clump stars: distances, intrinsic widths and stellar densities
• A comprehensive view of the Virgo Stellar Stream
• The Origin of the Virgo Stellar Substructure
• The Chemistry of the Trailing arm of the Sagittarius Dwarf Galaxy
• Kinematics & Chemistry of Halo Substructures: The Vicinity of the Virgo Over-Density
• Selecting Sagittarius: Identification and Chemical Characterization of the Sagittarius Stream