  The observed luminosity function (LF) of satellite galaxies shows several
interesting features that require a better understanding of gas-thermodynamic
processes and feedback effects related to reionization and galaxy formation. In
galaxy clusters, the abundance of dwarf galaxies is in good agreement with the
expectation based on the subhalo mass function, whereas in galaxy groups, the
relatively small abundance of dwarfs conflicts with theoretical expectations.
In all halo systems, there is a dip in the abundance of galaxies with
luminosities in the range ~ 2x10^8 L_sun to 10^10 L_sun, corresponding to
subhalo mass scales between ~ 5x10^10 M_sun to few times 10^11 M_sun.
Photoionization from reionization has been used to explain statistics of the
dwarf population, with larger systems forming prior to, and smaller systems
forming subsequent to, reionization. The observed dip in the LF is an imprint
of small dwarf galaxies (<2x10^8 L_sun) that formed prior to reionization. The
galactic winds powered by supernovae in these dwarf galaxies propagate energy
and metals to large distances such that the intergalactic medium is uniformly
enriched to a level of 10^-3 zsun, as observed in the low-redshift Ly-alpha
forest. The associated energy related to this metallicity raises the
intergalactic medium temperature and the Jeans mass to a range 10^10-10^11
M_sun at z ~ 3.4-6.0. Because the epoch of nonlinearity for halos in this mass
range is at z > 3.4-4.4, their gas content, hence star formation, is greatly
suppressed on average and leads to a dip in the observed LF at $z=0$. Larger
halos (M > 10^11 M_sun), becoming nonlinear at z < 3.4-4.4, have masses topping
the Jeans mass, where subhalo mass function based LF is again in agreement with
observations.
