Properties of Galaxies in and Around Voids

Abstract

Two surveys for intrinsically faint galaxies towards nearby voids have been conducted at the MPI für Astronomie, Heidelberg. One selected targets from a new diameter limited (Φ ≥ 5 ′′ ) catalog with morphological criteria while the other used digitized objective prism Schmidt plates to select mainly HII dwarf galaxies. For some 450 galaxies, redshifts and other optical data were obtained. We studied the spatial distribution of the sample objects, their luminosity function, and their intrinsic properties.Most of the galaxies belong to already well known sheets and filaments. But we found about a dozen highly isolated galaxies in each sample (nearest neighborhood distance ≥ 3h −1 75 M pc). These tend to populate additional structures and are not distributed homogeneously throughout the voids. As our results on 'void galaxies' still suffer from small sample statistics, I also tried to combine similar existing surveys of nearby voids to get further hints on the larger structure and on the luminosity function of the isolated galaxies. No differences in the luminosity function of sheet and void galaxies could be found.The optical and infrared properties of both samples are in the normal range for samples dominated by late-type dwarfs. Follow-up HI studies show that the isolated dwarfs in both samples have unusual high amount of neutral gas for a given luminosity.

Studies of galaxies in voids

“…One of the detailed, but somewhat limited (on galaxy number) studies of void low-mass galaxies is the Heidelberg void survey (Hopp et al 1995;Popescu et al 1996Popescu et al , 1997aPopescu et al , 1997bPopescu et al , 1998Hopp 1998). In the Hopp et al sample in the direction of voids only nine dwarf galaxies are located fully within voids (three objects), or in some intermediate regions near the void boundaries (six galaxies).…”