Journal Article

A 10 000 star spectroscopic survey of the thick disc–halo interface: phase-space sub-structure in the thick disc

Apoorva Jayaraman, Gerard Gilmore, Rosemary F. G. Wyse, John E. Norris and Vasily Belokurov

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 431, issue 1, pages 930-953
Published in print May 2013 | ISSN: 0035-8711
Published online March 2013 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1093/mnras/stt221
A 10 000 star spectroscopic survey of the thick disc–halo interface: phase-space sub-structure in the thick disc

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We analyse a 10 000 star spectroscopic survey, focused on Galactic thick disc stars typically 2–5 kpc from the Sun, carried out using the AAOmega Spectrograph on the Anglo-Australian Telescope (AAT). We develop methods for completeness correction of the survey based on Sloan Digital Sky Survey (SDSS) photometry, and we derive star distances using an improved isochrone fitting method with accuracies better than 10 per cent. We determine the large-scale kinematic [Vϕ = 172 km s−1 and σ(ϕ, r, z) = (49,51,40) km s−1], and abundance properties of the thick disc, 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 disc, localized 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 disc asymmetry.

Keywords: surveys; Galaxy: abundances; Galaxy: disc; Galaxy: kinematics and dynamics; Galaxy: stellar content

Journal Article.  16162 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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