Journal
ASTRONOMY & ASTROPHYSICS
Volume 535, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201117373
Keywords
Galaxy: evolution; Galaxy: kinematics and dynamics; stars: abundances; methods: observational
Categories
Funding
- Centre National d'Etudes Spatiales (CNES)
- Centre National de Recherche Scientifique (CNRS)
- Proyecto Fondecyt [1110393]
- Fondap Center for Astrophysics [15010003]
- BASAL CATA [PFB-06]
- Programa Iniciativa Cientifica Milenio [P07-021-F]
- Science and Technology Facilities Council [ST/H00243X/1] Funding Source: researchfish
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Context. In the era of large spectroscopic surveys, Galactic archaeology aims to understand the formation and evolution of the Milky Way by means of large datasets. In particular, the kinematic and chemical study of the thick disc can give valuable information on the merging history of the Milky Way. Aims. Our aim is to detect and characterise the Galactic thick disc chemically and dynamically by analysing F, G, and K stars, whose atmospheres reflect their initial chemical composition. Methods. We performed a spectroscopic survey of nearly 700 stars probing the Galactic thick disc far from the solar neighbourhood towards the Galactic coordinates (l similar to 277 degrees, b similar to 47 degrees). The derived effective temperatures, surface gravities and overall metallicities were then combined with stellar evolution isochrones, radial velocities and proper motions to derive the distances, kinematics and orbital parameters of the sample stars. The targets belonging to each Galactic component (thin disc, thick disc, halo) were selected either on their kinematics or according to their position above the Galactic plane, and the vertical gradients were also estimated. Results. We present here atmospheric parameters, distances and kinematics for this sample and a comparison of our kinematic and metallicity distributions with the Besan on model of the Milky Way. The thick disc far from the solar neighbourhood is found to differ only slightly from the thick disc properties as derived in the solar vicinity. For regions where the thick disc dominates (1 less than or similar to Z less than or similar to 4 kpc), we measured vertical velocity and metallicity trends of partial derivative V-phi/partial derivative Z = 19 +/- 8 km s(-1) kpc(-1) and partial derivative[M/H]/partial derivative Z = -0.14 +/- 0.05 dex kpc(-1), respectively. These trends can be explained as a smooth transition between the different Galactic components, although intrinsic gradients could not be excluded. In addition, a correlation partial derivative V-phi/partial derivative[M/H] = -45 +/- 12 km s(-1) dex(-1) between the orbital velocity and the metallicity of the thick disc is detected. This gradient is inconsistent with the SDSS photometric survey analysis, which did not detect any such trend, and challenges radial migration models of thick disc formation. Estimations of the scale heights and scale lengths for different metallicity bins of the thick disc result in consistent values, with h(R) similar to 3.4 +/- 0.7 kpc, and h(Z) similar to 694 +/- 45 pc, showing no evidence of relics of destroyed massive satellites.
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