Galaxy groups in the 2dF redshift survey: The catalogue

Abstract

We construct a galaxy groups catalogue from the public 100K data release of the 2dF galaxy redshift survey. The group identification is carried out using a slightly modified version of the group finding algorithm developed by Huchra & Geller. Several tests using mock catalogues allow us to find the optimal conditions to increase the reliability of the final group sample. A minimum number of 4 members, an outer number density enhancement of 80 and a linking radial cutoff of $200 km sec^{-1}$, are the best obtained values from the analysis. Using these parameters, approximately 90% of groups identified in real space have a redshift space counterpart. On the other hand the level of contamination in redshift space reaches to 30 % including a $\sim 6$ of artificial groups and $\sim 24$ of groups associated with binaries or triplets in real space. The final sample comprise 2209 galaxy groups covering the sky region described by Colless et al. spanning over the redshift range of $0.003 \leq z \leq 0.25$ with a mean redshift of 0.1.Comment: Accepted for publication in the MNRAS. 8 figures 8 page