Properties of voids in the Local Volume

TL;DR

This study compares observed galaxy voids in the Local Volume with simulations, suggesting halos below 45 km/s do not host galaxies, explaining the dark matter subhalo overabundance issue.

Contribution

It provides observational evidence and simulation analysis supporting a halo mass threshold for galaxy hosting in the Local Volume.

Findings

Observed void sizes range from 1 to 5 Mpc.

Theoretical void function matches observations for halos with V_c > 45 km/s.

Small voids are truly dark, lacking galaxies.

Abstract

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 ~ 30 voids with sizes ranging from 1 to 5 Mpc. We also 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 +/- 10 km/s. This agrees with the Local Group predictions. Small voids look quite similar to heir giant cousins: the density has a minimum at the center of a void and it increases as we get closer to the border. Thus, both the Local Group data and the nearby voids indicate that isolated halos below 45 +/- 10 km/s must not host galaxies and that small (few Mpc) voids are truly dark.