Astron. Astrophys. 325, 881-892
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Results of a search for emission-line galaxies towards nearby voids. The spatial distribution
Cristina C. Popescu1,3, Ulrich Hopp1,2, and Hans Elsässer1
1Max Planck Institut für Astronomie, Königstuhl 17,
D-69117 Heidelberg, Germany
Received 20 March 1997 / Accepted 16 April 1997
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)(Hagen et al. 1995) - 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 . The relevant brightness parameters of the sample are: (1) the sum of the flux in the emission-lines and of the continuum flux under the line, and (2) the equivalent widths (EW); the corresponding completeness limits are 6.7 10-14 erg sec -1 cm-2 and 8 Å, respectively.
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.
Key words: large scale structure - galaxies - redshift survey - galaxies: clusters - galaxies: compact
Send offprint requests to: Cristina C. Popescu
© European Southern Observatory (ESO) 1997
Online publication: September 9, 1997