Results of a search for emission-line galaxies towards nearby voids. The spatial distribution

TL;DR

This study searches for faint emission-line galaxies in nearby voids, revealing that while both ELGs and normal galaxies trace large-scale structures, some ELGs exist within voids, suggesting a non-homogeneous distribution.

Contribution

It provides the first detailed analysis of the spatial distribution of faint ELGs in voids, highlighting their presence within these underdense regions and challenging the idea of a homogeneous void galaxy population.

Findings

ELGs are found within nearby voids, including very well-defined ones.

Both ELGs and normal galaxies trace the same large-scale structures.

The distribution suggests voids are not completely empty of galaxies.

Abstract

We present the results of a search for emission-line galaxies (ELGs) towards nearby voids, based on a sample selected on the HQS (Hamburg Quasar Survey) - III-aJ objective-prism plates. The survey was based on the presence of emission-lines and therefore has the advantage to detect very faint objects (with all the flux in the emission-lines and almost no continuum), that would be missed by an apparent magnitude limited survey. We found objects as faint as B=20.5 and M(B)=(-15.0,-12.0). The observational data are given in Popescu et al. (1996) and in the present paper we consider a complete subsample from these data. We analyse the spatial distribution of our sample of ELGs in comparison with the distribution of normal galaxies. Overall both distributions trace the same structures. Nevertheless we also found a few ELGs in voids, from which at least 8 lie in the very well defined nearby voids. The isolated galaxies seem to form fainter structures that devide the larger voids into smaller ones. {}From our estimates of the expected number of void galaxies we conclude that we did not find an underlying homogenous void population.