Three-Dimensional Identification and Reconstruction of Galaxy Systems within Deep Redshift Surveys

Abstract

We have developed a new geometrical method for identifying and reconstructing a homogeneous and highly complete set of galaxy groups in the next generation of deep, flux-limited redshift surveys. Our method combines information from the three-dimensional Voronoi diagram and its dual, the Delaunay triangulation, to obtain group and cluster catalogs that are remarkably robust over wide ranges in redshift and degree of density enhancement. Using the mock DEEP2 catalogs, we demonstrate that the VDM algorithm can be used to identify a homogeneous set of groups in a magnitude-limited sample ($I\sbr{AB}\le23.5$) throughout the survey redshift window $0.7 < z < 1.2$. The actual group membership can be effectively reconstructed even in the distorted redshift space environment for systems with line of sight velocity dispersion $σ_{los}$ greater than $\approx 200$ \kms. By comparing the galaxy cluster catalog derived from the mock DEEP2 observations to the underlying distribution of clusters found in real space with much fainter galaxies included (which should more closely trace mass in the cluster), we can assess completeness in velocity dispersion directly. We conclude that the recovered DEEP2 group and cluster sample should be statistically complete for $σ_{los} \gtrsim 400$ \kms. Finally, we argue that the reconstructed bivariate distribution of systems as a function of redshift and velocity dispersion reproduces with high fidelity the underlying real space distribution and can thus be used robustly to constrain cosmological parameters