Cosmicflows-3: Cosmography of the Local Void

Abstract

Cosmicflows-3 distances and inferred peculiar velocities of galaxies have permitted the reconstruction of the structure of overdensities and underdensities within the volume extending to 0.05 c . This study focuses on the underdense regions, particularly the Local Void that lies largely in the zone of obscuration and consequently has received limited attention. Major overdense structures that bound the Local Void are the Perseus-Pisces and Norma-Pavo-Indus filaments separated by 8500 km s −1 . The void network of the universe is interconnected and void passages are found from the Local Void to the adjacent very large Hercules and Sculptor voids. Minor filaments course through voids. A particularly interesting example connects the Virgo and Perseus clusters, with several substantial galaxies found along the chain in the depths of the Local Void. The Local Void has a substantial dynamical effect, causing a deviant motion of the Local Group of 200–250 km s −1 . The combined perturbations due to repulsion from the Local Void and attraction toward the Virgo Cluster account for ∼50% of the motion of the Local Group in the rest frame given by the cosmic microwave background.