Voids in the Local Volume: a limit on appearance of a galaxy in a DM halo

TL;DR

This study investigates the distribution of voids in the Local Volume to test the hypothesis that only halos above a certain mass can host galaxies, finding a cutoff around 45 km/s consistent with observations.

Contribution

It provides observational evidence and simulation results supporting a halo mass threshold for galaxy formation in voids, refining our understanding of galaxy-dark matter halo relations.

Findings

Void sizes range from 1 to 5 Mpc with no galaxies present.

Halos with circular velocities below 45 km/s do not host luminous matter.

Small voids are dark and contain nonluminous halos forming a filamentary web.

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 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 +/- 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 +/- 10 km/s must not host galaxies and that small (few Mpc) voids are truly dark.