A LIGHT, CENTRALLY CONCENTRATED MILKY WAY HALO?

We discuss a novel approach to weighing the Milky Way (MW) dark matter halo, one that combines the latest samples of halo stars selected from the Sloan Digital Sky Survey (SDSS) with state of the art numerical simulations of MW analogs. The fully cosmological runs employed in the present study include Eris, one of the highest resolution hydrodynamical simulations of the formation of a M-vir = 8 x 10(11) M-circle dot late-type spiral, and the darkmatter-only M-vir = 1.7 x 10(12) M-circle dot Via Lactea II (VLII) simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and we successfully compare their density, velocity anisotropy, and radial velocity dispersion profiles with the observational data. Most mock SDSS realizations show the same cold veil recently observed in the distant stellar halo of the MW, with tracers as cold as sigma(los) approximate to 50 km s(-1) between 100 and 150 kpc. Controlled experiments based on the integration of the spherical Jeans equation as well as a particle tagging technique applied to VLII show that a heavy M-vir approximate to 2 x 10(12) M-circle dot realistic host produces a poor fit to the kinematic SDSS data. We argue that these results offer added evidence for a light, centrally concentrated MW halo.