  We use a semi-analytical model to study the impact of reionization, and the
associated radiative feedback, on galaxy formation. Two feedback models have
been considered: (i) a standard prescription, according to which star formation
is totally suppressed in galaxies with circular velocity below a critical
threshold (model CF06) and (ii) a characterization based on the filtering scale
(model G00), allowing for a gradual reduction of the gas available for star
formation in low-mass galaxies. In model CF06 reionization starts at z ~ 15-20,
is 85% complete by z ~ 10; at the same z, the ionized fraction is 16% in model
G00. The models match SDSS constraints on the evolution of the neutral hydrogen
fraction at z < 7, but predict different Thomson optical depths, tau_e = 0.1017
(CF06), and 0.0631 (G00); such values are within 1 sigma of the WMAP 3-yr
determination. Both models are in remarkable good agreement with additional
existing data (evolution of Lyman-limit systems, cosmic star formation history,
high-z galaxy counts, IGM thermal history), which therefore cannot be used to
discriminate among different feedback models. Deviations among radiative
feedback prescriptions emerge when considering the expected HI 21 cm background
signal, where a ~ 15 mK absorption feature in the range 75-100 MHz is present
in model G00 and a global shift of the emission feature preceding reionization
towards larger frequencies occurs in the same model. Single dish observations
with existing or forthcoming low-frequency radio telescopes can achieve mK
sensitivity, allowing the identification of these features provided that
foregrounds can be accurately subtracted.
