The effect of reionization of the intergalactic medium of galaxy formation

The reheating which accompanies reionization exerts a negative feedback effect on small‐scale structure formation. To illustrate this, we simulate the formation of structure on galactic and sub‐galactic scales in the mixed Cold+Hot Dark Matter (CHDM) model, utilizing our new Adaptive SPH method. We compare the rates of structure formation in a universe which is reionized and reheated at some epoch z≳5 (as required to satisfy the H I Gunn‐Peterson (GP) constraint on the IGM at z<5) to the rate of structure formation in a universe without such reheating. These results have strong implications for the comparison of the CHDM model with the observed abundance of damped Ly alpha clouds and the total H I content of the universe at z≳3.