A 10,000 star spectroscopic survey of the thick disk-halo interface : Phase-space sub-structure in the thick disk

Abstract

We analyse a 10,000 star spectroscopic survey, focused on Galactic thick disk stars typically 2-5 kpc from the Sun, carried out using the AAOmega Spectrograph on the AAT. We develop methods for completeness-correction of the survey based on SDSS photometry, and we derive star distances using an improved isochrone-fitting method with accuracies better than 10%. We determine the large-scale kinematic (Vphi=172 km/s and sigma(phi,r,z) = (49,51,40) km/s), and abundance properties of the thick disk, showing these representative values are a fair description within about 3 kpc of the sun, and in the range 1-3 kpc from the Galactic Plane. We identify a substantial overdensity in lines of sight towards the inner Galaxy, with metallicity [Fe/H] -1 dex, and higher line of sight velocities than the thick disk, localised along the direction (l,b)=(48,-26). This overdensity appears to be towards, but closer than, the known Hercules-Aquila halo overdensity and may be related to the Humphreys-Larsen inner galaxy thick disk asymmetry.

25 Pages, 26 Figures, Accepted by MNRAS

References in corpus (7)

• The Dartmouth Stellar Evolution Database
• The Milky Way Tomography with SDSS: II. Stellar Metallicity
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• The Hercules-Aquila Cloud
• The Age of the Milky Way Inner Halo
• Galactic Globular and Open Clusters in the Sloan Digital Sky Survey. II. Test of Theoretical Stellar Isochrones
• Searching for the metal-weak thick disc in the solar neighbourhood

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• Age Gradients Throughout the Galaxy with O-Miras
• The Escape Velocity Curve of the Milky Way in Modified Newtonian Dynamics
• The kinematics of local thick discs do not support an accretion origin
• The imprints of the Galactic bar on the thick disk with RAVE
• Dynamical History Of The Local Group In $\Lambda$CDM $\mathrm{II}$ $-$ Including External Perturbers In 3D