The asymptotic tidal remnants of cold dark matter subhalos
  We use N-body simulations to study the evolution of cuspy cold dark matter
(CDM) halos in the gravitational potential of a massive host. Tidal mass losses
reshape CDM halos, leaving behind bound remnants whose characteristic densities
are set by the mean density of the host at the pericentre of their respective
orbit. The evolution to the final bound remnant state is essentially complete
after ~5 orbits for nearly circular orbits, while reaching the same remnant
requires ~25 and ~40 orbits for eccentric orbits with 1:5 and 1:20
pericentre-to-apocentre ratios, respectively. The density profile of tidal
remnants is fully specified by the fraction of mass lost, and approaches an
exponentially-truncated Navarro-Frenk-White profile in the case of heavy mass
loss. Resolving tidal remnants requires excellent numerical resolution; poorly
resolved subhalos have systematically lower characteristic densities and are
more easily disrupted. Even simulations with excellent spatial and time
resolution fail when the final remnant is resolved with fewer than 3000
particles. We derive a simple empirical model that describes the evolution of
the mass and the density profile of the tidal remnant applicable to a wide
range of orbital eccentricities and pericentric distances. Applied to the Milky
Way, our results suggest that $10^8$ - $10^{10}$ solar mass halos accreted ~10
Gyrs ago on 1:10 orbits with pericentric distance ~10 kpc should have been
stripped to 0.1 - 1 per cent of their original mass. This implies that
estimates of the survival and structure of such halos (the possible hosts of
ultra-faint Milky Way satellites) based on direct cosmological simulations may
be subject to substantial revision.
