Metallicity Bias in the Kinematics of the Milky Way Stellar Halo
  Here we study the metallicity bias in the velocity dispersions, the derived
quantity called anisotropy and the mean azimuthal velocity profiles of the
Milky Way stellar halo using Blue Horizontal Branch (BHB) stars taken from
SDSS/SEGUE survey. The comparatively metal-rich sample ([Fe/H]>-2) has prograde
motion and is found to have an offset of 40 km/s in the mean azimuthal velocity
with respect to a metal-poor sample ([Fe/H]<=-2) which has retrograde motion.
The difference in rotation between the most metal-poor and most metal-rich
population was found to be around 65 km/s. For galactocentric distances r<16
kpc, an offset in velocity dispersion profiles and anisotropy can also be seen.
In the inner regions, the metal-poor population is in average tangential orbit;
however, anisotropy is found to decrease monotonically with radius independent
of metallicity. Beyond r = 16 kpc, both the metal-rich and the metal-poor
samples are found to have tangential motion. The metallicity bias in the
kinematics of the halo stars qualitatively supports the co-existence of at
least two-components in the halo having different formation history e.g.
in-situ formation and formation by accretion.
