Effect of Reionization on the Structure Formation in the Universe

I use the simulations of cosmological reionization to quantify the effect of the gas fraction suppression in the low density objects due to photoionization. I show that the Jeans mass does not match the characteristic mass scale below which the gas is efficiently expelled from the shallow potential wells, and which can be orders of magnitude lower that the Jeans mass. Instead, the filtering mass, that directly corresponds to the filtering scale over which the baryonic perturbations are smoothed in the linear theory, provides a remarkably good fit to the characteristic mass scale. I also derive the full shape of the probability distribution to find an object with a given gas mass among all the objects with the same total mass which depends exclusively on the filtering mass. The proposed probability distribution may be useful for semi-analytical modeling of structure formation in the universe. Subject headings: cosmology: theory cosmology: large-scale structure of universe galaxies: formation galaxies: intergalactic medium