We present a new method for generating initial conditions for \Lambda CDM 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 } < 10 ^ { 5 } L _ { \odot } , 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 ( \Sigma _ { V } ) < -1.4 .
We estimate that the region outside R _ { 50 } ( \sim 400 kpc ) up to 1 Mpc from the Milky Way contains about a hundred true fossils of the first galaxies with V-band luminosity 10 ^ { 3 } -10 ^ { 5 } L _ { \odot } and half-light radii , r _ { hl } \sim 100 - 1000 pc .