A Kinematically-Distinct RR-Lyrae Overdensity in the Inner Regions of the Milky Way

Abstract

We combine the Siding Spring Survey of RR Lyrae stars with the Southern Proper Motion Catalog 4, in order to detect and kinematically characterize overdensities in the inner halo of the Milky Way. We identify one such overdensity above the Galactic plane, in quadrant 4 of the Galaxy. The overdensity extends at least 20 degrees in longitude, has an average heliocentric distance of 8 kpc with a depth of 4 kpc, and is confined within 4 kpc of the Galactic plane. Its metallicity distribution is distinct from that of the field population having a peak at -1.3 and a pronounced tail to -2.0. Proper motions indicate a net vertical motion away from the plane, and a low orbital angular momentum. Qualitatively, these orbit properties suggest a possible association with omega Centauri's parent satellite. However, comparison to a specific omega Cen N-body disruption model does not give a good match with observations. Line-of-sight velocities, and more extensive N-body modelling will help clarify the nature of this overdensity.

Accepted for publication in Astrophysical Journal Letters

References in corpus (5)

• The Structure of the Milky Way's Bar Outside the Bulge
• The QUEST RR Lyrae Survey II: The Halo Overdensities in the First Catalog
• Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys
• No Excess of RR Lyrae Stars in the Canis Major Overdensity
• Resonant Trapping in the Galactic Disc and Halo and its Relation with Moving Groups

Cited by in corpus (1)

• rrlfe: Software for Generating and Applying Metallicity Calibrations for RR Lyrae Variable Stars Across a Wide Range of Phases and Temperatures