2011ApJ...741...17B

We present a new method for generating initial conditions for ΛCDM N-body simulations which provides the dynamical range necessary to follow the evolution and distribution of the fossils of the first galaxies on Local Volume, 5-10 Mpc, scales. The initial distribution of particles represents the position, velocity, and mass distribution of the dark and luminous halos extracted from pre-reionization simulations. We confirm previous results that ultra-faint dwarfs have properties compatible with being well-preserved fossils of the first galaxies. However, because the brightest pre-reionization dwarfs form preferentially in biased regions, they most likely merge into non-fossil halos with circular velocities >20-30 km/s. Hence, we find that the maximum luminosity of true fossils in the Milky Way is L_V< 10⁶ L_{x2609}, casting doubts on the interpretation that some classical dSphs are true fossils. In addition, we argue that most ultra-faints at small galactocentric distance, R < 50 kpc, had their stellar properties modified by tides, while a large population of fossils is still undetected due to their extremely low surface brightness log (Σ_V) < -1.4. We estimate that the region outside R₅₀(∼400 kpc) up to 1 Mpc from the Milky Way contains about a hundred true fossils of the first galaxies with V-band luminosity 10³-10⁵ L_{x2609} and half-light radii, r_hl∼ 100-1000 pc.