THE STRUCTURE OF SUPERVOIDS .1. VOID HIERARCHY IN THE NORTHERN LOCAL SUPERVOID

Supervoids are regions in the local Universe which do not contain rich clusters of galaxies. In order to investigate the distribution of gal axies in and around supervoids, we have studied the closest example, t he Northern Local Void. It is defined as the region between the Local, Coma, and the Hercules superclusters, which is well covered by availa ble redshift surveys. We find that this supervoid is not empty, but it contains small galaxy systems and poor clusters of galaxies. We study the cosmography of this void by analyzing the distribution of poor cl usters of galaxies, elliptical and other galaxies in two projections. We present a catalogue of voids, defined by galaxies of different morp hological type and luminosity, and analyze mean diameters of voids in different environments. This analysis shows that sizes of voids and pr operties of void walls are related. Voids:defined by poor clusters of galaxies and by bright elliptical galaxies have a mean diameter of up to 40 h(-1) Mpc. Faint late-type galaxies divide these voids into smal ler voids. The faintest galaxies we can study are outlining voids with mean diameters of about 8 h(-1) Mpc. Voids located in a high-density environment are smaller than voids in low-density regions. The depende nce of void diameters on the type and luminosity of galaxies, as well as on the large-scale environment shows that voids form a hierarchical system.