Volume 510, February 2010
|Number of page(s)||5|
|Published online||11 February 2010|
Letter to the Editor
Evidence of a thick disk rotation–metallicity correlation
INAF-Osservatorio Astronomico di Torino,
via Osservatorio 20, 10025 Pino Torinese, Italy e-mail: firstname.lastname@example.org
2 University of Ljubljana, Faculty of Mathematics and Physics, Jadranska 19, SLO-1000 Ljubljana, Slovenia
Accepted: 13 January 2010
We analyze a new kinematic survey that includes accurate proper motions derived from SDSS DR7 positions, combined with multi-epoch measurements from the GSC-II database. By means of the SDSS spectro-photometric data (effective temperature, surface gravity, metallicity, and radial velocities), we estimate photometric parallaxes for a sample of 27 000 FGK (sub)dwarfs with [Fe/H] < -0.5, which we adopted as tracers of the seven-dimensional space distribution (kinematic phase distribution plus chemical abundance) of the thick disk and inner halo within a few kiloparsecs of the Sun. We find evidence of a kinematics-metallicity correlation, km s-1 dex-1, amongst thick disk stars located between one and three kiloparsecs from the plane and with abundance -1 < [Fe/H] < -0.5, while no significant correlation is present for [Fe/H] -0.5. In addition, we estimate a shallow vertical rotation velocity gradient, km s-1 kpc-1, for the thick disk between 1 kpc < |z| < 3 kpc, and a low prograde rotation, 37 ± 3 km s-1 for the inner halo up to 4 kpc. Finally, we briefly discuss the implications of these findings for the thick disk formation scenarios in the context of CDM hierarchical galaxy formation mechanisms and of secular evolutionary processes in galactic disks.
Key words: Galaxy: disk / Galaxy: kinematics and dynamics / Sun: abundances / stars: kinematics and dynamics / surveys
© ESO, 2010
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