The stellar halo in the inner Milky Way: predicted shape and kinematics

We have used N-body simulations for the MilkyWay to investigate the kinematic and structural properties of the old metal-poor stellar halo in the barred inner region of the Galaxy. We find that the extrapolation of the density distribution for bulge RR Lyrae stars, rho similar to r(-3), approximately matches the number density of RR Lyrae in the nearby stellar halo. We follow the evolution of such a tracer population through the formation and evolution of the bar and box/peanut bulge in the N-body model. We find that its density distribution changes from oblate to triaxial, and that it acquires slow rotation in agreement with recent measurements. The maximum radial velocity is similar to 15-25 km s(-1) at |l| = 10 degrees-30 degrees, and the velocity dispersion is similar to 120 km s(-1). Even though the simulated metal-poor halo in the bulge has a barred shape, just 12 per cent of the orbits follow the bar, and it does not trace the peanut/X structure. With these properties, the RR Lyrae population in the Galactic bulge is consistent with being the inward extension of the Galactic metal-poor stellar halo.