Evidence of a thick disk rotation-metallicity correlation
  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, dVphi/d[Fe/H]=40-50 km/s/dex, 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, dVphi/d|z| = -19 +/- 2 km/s/kpc, for the thick disk between 1 kpc <
|z| < 3 kpc, and a low prograde rotation, 37 +/- 3 km/s 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.
