Galaxy groups in the 2dFGRS: the group-finding algorithm and the 2PIGG catalogue (original) (raw)

Galaxy groups in the 2dF redshift survey: The catalogue

2002

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 real space have a redshift space counterpart. On the other hand the level of contamination in redshift space reaches to 30 artificial groups and ∼ 24 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 ≤ z ≤ 0.25 with a mean redshift of 0.1.

Groups of Galaxies in the Two Micron All-Sky Redshift Survey

Astrophysical Journal, 2006

We present the results of applying a percolation algorithm to the initial release of the Two Micron All-Sky Survey Extended Source Catalog, using subsequently measured redshifts for almost all of the galaxies with K < 11.25 mag. This group catalog is based on the first near-IR all-sky flux-limited survey that is complete to |b| = 5 deg. We explore the dependence of the clustering on the length and velocity scales involved. The paper describes a group catalog, complete to a limiting redshift of 10,000 km/s, created by maximizing the number of groups containing 3 or more members. A second catalog is also presented, created by requiring a minimum density contrast of 80 to identify groups. We identify known nearby clusters in the catalogs and contrast the groups identified in the two catalogs. We examine and compare the properties of the determined groups and verify that the results are consistent with the UZC-SSRS2 and northern CfA redshift survey group catalogs. The all-sky nature of the catalog will allow the development of a flow-field model based on the density field inferred from the estimated cluster masses.