We present a detailed analysis of the space motions of 1203 solar-neighborhood stars with metal abundances { [ Fe / H ] } \leq - 0.6 , on the basis of a recently revised and supplemented catalog of metal-poor stars selected without kinematic bias ( Beers et al .
2000 ) .
This sample , having available proper motions , radial velocities , and distance estimates for stars with a wide range of metal abundances , is by far the largest such catalog to be assembled to date .

We show that the stars in our sample with [ Fe/H ] \leq - 2.2 , which likely represent a “ pure ” halo component , are characterized by a radially elongated velocity ellipsoid ( \sigma _ { U } , \sigma _ { V } , \sigma _ { W } ) = ( 141 \pm 11 , 106 \pm 9 , 94 \pm 8 ) km s ^ { -1 } and small prograde rotation < V _ { \phi } > = 30 to 50 km s ^ { -1 } , consistent with previous analysis of this sample based on radial velocity information alone ( Beers & Sommer-Larsen 1995 ) .
In contrast to the previous analysis , we find a decrease in < V _ { \phi } > with increasing distance from the Galactic plane for stars which are likely to be members of the halo population ( \Delta < V _ { \phi } > / \Delta|Z| = -52 \pm 6 km s ^ { -1 } kpc ^ { -1 } ) , which may represent the signature of a dissipatively formed flattened inner halo .

Unlike essentially all previous kinematically selected catalogs , the metal-poor stars in our sample exhibit a diverse distribution of orbital eccentricities , e , with no apparent correlation between [ Fe/H ] and e .
This demonstrates , clearly and convincingly , that the evidence offered by Eggen , Lynden-Bell , and Sandage ( 1962 ) for a rapid collapse of the Galaxy , an apparent correlation between the orbital eccentricity of halo stars with metallicity , is basically the result of their proper-motion selection bias .
However , even in our non-kinematically selected sample , we have identified a small concentration of high- e stars at [ Fe/H ] \sim - 1.7 , which may originate , in part , from infalling gas during the early formation of the Galaxy .

We find no evidence for an additional thick disk component for stellar abundances [ Fe/H ] \leq - 2.2 .
The kinematics of the intermediate-abundance stars close to the Galactic plane are , in part , affected by the presence of a rapidly rotating thick disk component with < V _ { \phi } > \simeq 200 km s ^ { -1 } ( with a vertical velocity gradient on the order of \Delta < V _ { \phi } > / \Delta|Z| = -30 \pm 3 km s ^ { -1 } kpc ^ { -1 } ) , and velocity ellipsoid ( \sigma _ { U } , \sigma _ { V } , \sigma _ { W } ) = ( 46 \pm 4 , 50 \pm 4 , 35 \pm 3 ) km s ^ { -1 } .
The fraction of low-metallicity stars in the solar neighborhood which are members of the thick disk population is estimated as \sim 10 \% for -2.2 < [ Fe/H ] \leq - 1.7 and \sim 30 \% for -1.7 < [ Fe/H ] \leq - 1 .
We obtain an estimate of the radial scale length of the metal-weak thick disk of 4.5 \pm 0.6 kpc .

We also analyze the global kinematics of the stars constituting the halo component of the Galaxy .
The outer part of the halo , which we take to be represented by local stars on orbits reaching more than 5 kpc from the Galactic plane , exhibits no systematic rotation .
In particular , we show that previous suggestions of the presence of a “ counter-rotating high halo ” are not supported by our analysis .
The density distribution of the outer halo is nearly spherical , and exhibits a power-law profile that is accurately described as \rho \propto R ^ { -3.55 \pm 0.13 } .
The inner part of the halo is characterized by a prograde rotation and a highly flattened density distribution .
We find no distinct boundary between the inner and outer halo .

We confirm the clumping in angular-momentum phase space of a small number of local metal-poor stars noted by Helmi et al .
( 1999 ) .
We also identify an additional elongated feature in angular-momentum phase space extending from the clump to regions with high azimuthal rotation .
The number of members in the detected clump is not significantly increased from that reported by Helmi et al. , even though the total number of the sample stars we consider is almost triple that of the previous investigation .
We conclude that the fraction of halo stars that may have arisen from the precursor object of this clump may be smaller than 10 % of the present Galactic halo , as previously suggested .

The implications of our results for the formation of the Galaxy are discussed , in particular in the context of the currently favored Cold Dark Matter theory of hierarchical galaxy formation .