THE THREE-DIMENSIONAL VELOCITY STRUCTURE OF THE THICK DISK FROM SPM4 AND RAVE DR2

We analyze the three-dimensional kinematics of a sample of similar to 4400 red clump stars ranging between 5 and 10 kpc from the Galactic center and up to 3 kpc from the Galactic plane. This sample is representative for the metal-rich ([Fe/H] = -0.6 - +0.5) thick disk. Absolute proper motions are from the fourth release of the Southern Proper Motion Program and radial velocities from the second release of the Radial Velocity Experiment. The derived kinematical properties of the thick disk include the rotational velocity gradient partial derivative V-theta/partial derivative z = -25.2 +/- 2.1 km s(-1) kpc(-1), velocity dispersions (sigma(VR), sigma(V theta), sigma(Vz))vertical bar (z = 1) = (70.4, 48.0, 36.2)+/-(4.1, 8.3, 4.0) km s(-1), and velocity-ellipsoid tilt angle alpha(Rz) = 8.degrees 6 +/- 1.degrees 8. Our dynamical estimate of the thin-disk scale length is R-thin = 2.0 +/- 0.4 kpc and of the thick-disk scale height is z(thick) = 0.7 +/- 0.1 kpc. The observed orbital eccentricity distribution compared with those from four different models of the formation of the thick disk from Sales et al. favors the gas-rich merger model and the minor merger heating model. Interestingly, when referred to the currently accepted value of the LSR, stars more distant than 0.7 kpc from the Sun show a net average radial velocity of 13 +/- 3 km s(-1). This result is seen in previous kinematical studies using other tracers at distances larger than similar to 1 kpc. We suggest this motion reflects an inward perturbation of the locally defined LSR induced by the spiral density wave.