Exploring the Sagittarius Stream with SEKBO Survey RR Lyrae Stars

Abstract

A sample of RR Lyrae (RRL) variables from the Southern Edgeworth-Kuiper Belt Object survey in regions overlapping the expected position of debris from the interaction of the Sagittarius (Sgr) dwarf galaxy with the Milky Way (RA ~ 20 and 21.5 h; distance 16-21 kpc) has been followed up spectroscopically and photometrically. The 21 photometrically confirmed type ab RRLs have mean [Fe/H] = -1.79 +/- 0.08, consistent with the abundances found for RRLs in a different portion of the Sgr tidal debris stream. The distribution of velocities in the Galactic standard of rest frame (V_GSR) of the 26 RRLs in the region is not consistent with a smooth halo population. Upon comparison with the Sgr disruption models of Law et al (2005), a prominent group of five stars having highly negative radial velocities (V_GSR ~ -175 kms-1) is consistent with predictions for old trailing debris when the Galactic halo is modeled as oblate. The observations also require that the recent trailing debris stream has a broader spread perpendicular to the Sgr plane than predicted by the models. We have also investigated the possible association of the Virgo Stellar Stream (VSS) with Sgr debris by comparing radial velocities for RRLs in the region with the same models, finding similarities in the velocity-position trends. As suggested by our earlier work, the stars in the VSS region with large negative V_GSR values are likely to be old leading Sgr debris, but we find that while old trailing Sgr debris may well make a contribution at positive V_GSR values, it is unlikely to fully account for the VSS feature. Overall we find that further modeling is needed, as trailing arm data generally favors oblate models while leading arm data favors prolate models, with no single potential fitting all the observed data.

42 pages, 13 Figures, accepted for publication in the Astrophysical Journal (Abstract is abridged version, full resolution figures available at http://www.mso.anu.edu.au/~gdc/papers/)

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Cited by in corpus (15)

• The Sagittarius Dwarf Galaxy: a Model for Evolution in a Triaxial Milky Way Halo
• The Sagittarius Streams in the Southern Galactic Hemisphere
• Constraints on the shape of the Milky Way dark matter halo from the Sagittarius stream
• Evidence for a Milky Way Tidal Stream Reaching Beyond 100 kpc
• A Two Micron All-Sky Survey View of the Sagittarius Dwarf Galaxy: VI. s-Process and Titanium Abundance Variations Along the Sagittarius Stream
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• The globular cluster system of the Milky Way: accretion in a cosmological context
• The Northern wraps of the Sagittarius Stream as traced by Red Clump stars: distances, intrinsic widths and stellar densities
• The Chemistry of the Trailing arm of the Sagittarius Dwarf Galaxy
• Kinematics & Chemistry of Halo Substructures: The Vicinity of the Virgo Over-Density
• STREGA: STRucture and Evolution of the GAlaxy. I. Survey Overview and First Results
• Main Sequence Star Populations in the Virgo Overdensity Region
• Order and chaos in a three dimensional galaxy model
• A fork in the Sagittarius trailing debris
• Metallicity and kinematical clues to the formation of the Local Group