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

TL;DR

This study analyzes a large spectroscopic survey of thick disk stars near the Sun, revealing their kinematic and chemical properties, and identifies a significant overdensity possibly linked to inner Galaxy structures.

Contribution

Developed a method for completeness correction and improved star distance estimation, providing detailed kinematic and abundance profiles of the thick disk within 3 kpc of the Sun.

Findings

Thick disk stars have Vphi=172 km/s and velocity dispersions (49,51,40) km/s.

Identified a metallicity [Fe/H] -1 dex overdensity towards the inner Galaxy.

Detected a kinematic overdensity possibly related to the inner Galaxy asymmetry.

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.