Automated Detection of Voids in Redshift Surveys

Abstract

We present a new void search algorithm for automated detection of voids in 3D redshift surveys. Based on a model in which the main features of the LSS of the Universe are voids and walls, we classify the galaxies into wall galaxies and field galaxies and we define voids as continuous volumes that are devoid of any wall galaxies. Field galaxies are allowed within the voids. The algorithm makes no assumptions regarding the shapes of the voids and the only constrain that is imposed is that the voids are always thicker than a preset limit, thus eliminating connections between adjacent voids through small breaches in the walls. By appropriate scaling using the selection function this algorithm can be used to analyze flux-limited surveys. We test the algorithm on Voronoi tessellations and apply it to the new SSRS2 redshift survey to derive the spectrum of void sizes and other void properties. We find that the average diameter of a void is 37 \\pm 8 h^{-1} Mpc. We suggest the usage of this fully automated algorithm to derive a void statistics, as another tool in describing the LSS of the Universe and for comparison with numerical simulations.