We study the formation and evolution of voids in the dark matter distribution using various simulations of the popular \Lambda Cold Dark Matter cosmogony .
We identify voids by requiring them to be regions of space with a mean overdensity of -0.8 or less – roughly the equivalent of using a Spherical Overdensity group finder for haloes .
Each of the simulations contains thousands of voids .
The distribution of void sizes in the different simulations shows good agreement when differences in particle and grid resolution are accounted for .
Voids very clearly correspond to minima in the smoothed initial density field .
Apart from a very weak dependence on the mass resolution , the rescaled mass profiles of voids in the different simulations agree remarkably well .
We find a universal void mass profile of the form \rho ( < r ) / \rho ( r _ { eff } ) \propto \exp [ ( r / r _ { eff } ) ^ { \alpha } ] where r _ { eff } is the effective radius of a void and \alpha \sim 2 .
The mass function of haloes in voids is steeper than that of haloes that populate denser regions .
In addition , the abundances of void haloes seem to evolve somewhat more strongly between redshifts \sim 1 and 0 than the global abundances of haloes .