Draining the Local Void

TL;DR

This study uses Hubble observations to measure the distances and motions of two dwarf galaxies within the Local Void, confirming they are moving away from the void center at several hundred km/s, supporting the void expansion hypothesis.

Contribution

First direct distance and velocity measurements of galaxies deep within the Local Void, providing empirical evidence for void expansion.

Findings

Galaxies are moving away from the void center at several hundred km/s.

Distances to the galaxies are approximately 8.4 Mpc and 7.0 Mpc.

Galaxies exhibit peculiar velocities consistent with void expansion.

Abstract

Two galaxies that lie deep within the Local Void provide a test of the expectation that voids expand. The modest (M_B~-14) HI bearing dwarf galaxies ALFAZOAJ1952+1428 and KK246 have been imaged with Hubble Space Telescope in order to study the stellar populations and determine distances from the luminosities of stars at the tip of the red giant branch. The mixed age systems have respective distances of 8.39 Mpc and 6.95 Mpc and inferred line-of-sight peculiar velocities of -114 km/s and -66 km/s toward us and away from the void center. These motions compound on the Milky Way motion of ~230 km/s away from the void. The orbits of the two galaxies are reasonably constrained by a numerical action model encompassing an extensive region that embraces the Local Void. It is unambiguously confirmed that these two void galaxies are moving away from the void center at several hundred km/s.