Constraints on the assembly history of the Milky Way's smooth, diffuse
  stellar halo from the metallicity-dependent, radially-dominated velocity
  anisotropy profiles probed with K giants and BHB stars using LAMOST,
  SDSS/SEGUE, and Gaia
  We analyze the anisotropy profile of the Milky Way's smooth, diffuse stellar
halo using SDSS/SEGUE blue horizontal branch stars and SDSS/SEGUE and LAMOST K
giants. These intrinsically luminous stars allow us to probe the halo to
approximately 100 kpc from the Galactic center. Line-of-sight velocities,
distances, metallicities, and proper motions are available for all stars via
SDSS/SEGUE, LAMOST, and Gaia, and we use these data to construct a full 7D set
consisting of positions, space motions, and metallicity. We remove substructure
from our samples using integrals of motion based on the method of Xue et al. We
find radially dominated kinematic profiles with nearly constant anisotropy
within 20 kpc, beyond which the anisotropy profile gently declines although
remains radially dominated to the furthest extents of our sample. Independent
of star type or substructure removal, the anisotropy depends on metallicity,
such that the orbits of the stars become less radial with decreasing
metallicity. For $-1.7<$ [Fe/H] $<-1$, the smooth, diffuse halo anisotropy
profile begins to decline at Galactocentric distances $\sim20$ kpc, from
$\beta\sim0.9$ to 0.7 for K giants and from $\beta\sim0.8$ to 0.1 for blue
horizontal branch stars. For [Fe/H] $<-1.7$, the smooth, diffuse halo
anisotropy remains constant along all distances with $0.2<\beta<0.7$ depending
on the metallicity range probed, although independent on star type. These
samples are ideal for estimating the total Galactic mass as they represent the
virialized stellar halo system.
