Differential rotation of the halo traced by the K-giant stars
  We use K-giant stars selected from the LAMOST DR5 to study the variation of
the rotational velocity of the galactic halo at different space positions.
Modelling the rotational velocity distribution with both the halo and disk
components, we find that the rotational velocity of the halo population
decreases almost linearly with increasing vertical distance to the galactic
disk plane, $Z$, at fixed galactocentric radius, $R$. The samples are separated
into two parts with
  $6<R<12$ kpc and $12<R<20$ kpc. We derive that the decreasing rates along $Z$
for the two subsamples are $-3.07\pm0.63$ and $-1.89\pm0.37$ km s$^{-1}$
kpc$^{-1}$, respectively. Compared with the TNG simulations, we suggest that
this trend is probably caused by the interaction between the disk and halo. The
results from the simulations show that only the oblate halo can provide a
decreasing rotational velocity with an increasing $Z$. This indicates that the
Galactic halo is oblate with galactocentric radius $R<20$ kpc. On the other
hand, the flaring of the disk component (mainly the thick disk) is clearly
traced by this study, with $R$ between 12 and 20 kpc, the disk can vertically
extend to $6\sim10$ kpc above the disk plane. What is more interesting is that,
we find the
  Gaia-Enceladus-Sausage (GES) component has a significant contribution only in
the halo with $R<12$ kpc, i.e. a fraction of 23$-$47\%. While in the outer
subsample, the contribution is too low to be well constrained.
