The tumultuous lives of galactic dwarfs and the missing satellites problem

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Abstract
Hierarchical Cold Dark Matter (CDM) models predict that Milky Way (MW) sized halos contain hundreds of dense low-mass dark satellites, an order of magnitude more than the number of observed satellites in the Local Group (LG). If the CDM paradigm is correct, we need to understand why most of these halos failed to form stars and become galaxies. We analyze the dynamical evolution of the satellite halos in a high-resolution cosmological simulation of MW sized halos in the LCDM cosmology. We find that about 10% of the substructure halos with the present masses 10^9 Msun) high-redshift systems, in which the gas could cool efficiently by atomic line emission and which were not significantly affected by the extragalactic ultraviolet radiation. We present a simple galaxy formation model based on the trajectories extracted from the simulation, which accounts for the bursts of star formation after strong tidal shocks and the inefficiency of gas cooling in halos with virial temperatures Tvir<~10^4 K. Our model reproduces the abundance, spatial distribution, and morphological segregation of the observed Galactic satellites. The results are insensitive to the redshift of reionization.

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