Galaxy Voids in Cold Dark Matter Universes

We present predictions for numerous statistics related to the presence of voids in the distribution of galaxies in a cold dark matter model of structure formation using a semi-analytic model of galaxy formation. Our study is able to probe galaxies with masses as low as 10^9Msun/h corresponding to absolute magnitudes of M_bJ-5log(h)=-18.1 and M_r-5log(h)=-18.7. We quantify the void and underdense probability functions, distributions of nearest neighbour distances and void sizes and compute the density profiles of voids. These results are contrasted with the expectations for dark matter (and the difference examined in terms of the galaxy/dark matter biasing relation) and are compared to analytic predictions and observational data where available. The predicted void probability functions are consistent with those measured from the Center for Astrophysics redshift surveys given the rather large uncertainties in this relatively small (for studies of voids) observational sample. The size of the observational sample is too small to probe the bias between galaxies and dark matter that we predict. We also examine the predicted properties of galaxies living within voids and contrast these with the general galaxy population. Our predictions are aimed at forthcoming large galaxy redshift surveys which should for the first time provide statistically accurate measures of the void population