Current explanation of the overabundance of dark matter subhalos in the Local Group ( LG ) indicates that there maybe a limit on mass of a halo , which can host a galaxy .
This idea can be tested using voids in the distribution of galaxies : at some level small voids should not contain any ( even dwarf ) galaxies .
We use observational samples complete to M _ { B } = -12 with distances less than 8 Mpc to construct the void function ( VF ) : the distribution of sizes of voids empty of any galaxies .
There are \sim 30 voids with sizes ranging from 1 to 5 Mpc .
We then study the distribution of dark matter halos in very high resolution simulations of the LCDM model .
The theoretical VF matches the observations remarkably well only if we use halos with circular velocities larger than 45 \pm 10 km/s .
This agrees with the Local Group predictions .
There are smaller halos in the voids , but they should not produce any luminous matter .
Small voids look quite similar to their giant cousins : the density has a minimum at the center of a void and it increases as we get closer to the border .
Small nonluminous halos inside the void form a web of tiny filaments .
Thus , both the Local Group data and the nearby voids indicate that isolated halos below 45 \pm 10 km/s must not host galaxies and that small ( few Mpc ) voids are truly dark .