Kinematics of Milky Way satellites in a Lambda cold dark matter universe

Abstract

We investigate whether the subhalos of Lambda-CDM galaxy halos have potentials consistent with the observed properties of Milky Way satellites, particularly those with high-quality photometric and kinematic data: Fornax, Leo I, Sculptor, Sextans, and Carina. We compare spherical models with isotropic velocity dispersion tensors to the observed, circularly averaged star counts, line-of-sight velocity dispersion profiles and line-of-sight velocity distributions. We identify subhalos within the six high-resolution dark matter halos of the Aquarius Project for which the spherically averaged potentials result in excellent fits to each of the five galaxies. In particular, our simple one-integral models reproduce the observations in the inner regions, proving that these data are fully consistent with Lambda-CDM expectations and do not require cored dark matter distributions. For four of the five satellites the fits require moderately cusped {\it stellar} density profiles. The star count data for Leo I, however, do require a cored distribution of star counts. Current data suggest that these five satellites may be hosted by Lambda-CDM subhalos with maximum circular velocities in the range 10 to 30 km/s.