Fading Features Found in the Kinematics of the Far-Reaching Milky Way Stellar Halo

We test the long-term kinematical stability of a Galactic stellar halo model, due to Kafle et al. (2012), who study the kinematics of approximately 5000 blue horizontal branch stars in the Sloan Digital Sky Survey. The velocity dispersion sigma and anisotropy parameter beta of the stars have been determined as functions of Galactocentric radius, over the range 6 < R-GC < 25 kpc, and show a strong dip in the anisotropy profile at R-GC similar to 17 kpc. By directly integrating orbits of particles in a 3D model of the Galactic potential with these characteristics, we show that the sigma and beta profiles quickly evolve on a time-scale of a few x 10 Myr whereas the density rho profile remains largely unaffected. We suggest that the feature is therefore transient. The origin of such features in the Galactic halo remains unclear.