Voids in Galaxy Redshift Surveys

Abstract

One of the most striking features in galaxy redshift surveys is the ubiquitous presence of voids. However, voids have not been extensively studied due to observational limitations. Until recently, galaxy redshift surveys included only a few voids of diameter > 30 h-1Mpc. The first step in studying voids is the identification process. We outline a method for detecting voids (based on the method of El-Ad and Piran 1997, EP97). We apply it to the PSCz survey, and the Updated Zwicky Catalog. We find that voids have typical diameters of ~30 h-1Mpc and are very underdense regions with (delta rho)/rho ~ -0.95. Up to 40% of volume of the Universe is occupied by voids. We discuss the results from these surveys and our detection algorithm's usefulness for future surveys. The next generation of surveys (such as the Sloan Digital Sky Survey and 2dFGRS) will improve this situation. The surveys will extend to greater depths, allowing a more statistically complete sample of voids to be obtained and the accompanying digital imaging will provide accurate photometry of fainter objects. This will allow us to gain greater insight into the nature of voids, search for possible void galaxies and maybe place constraints on cosmological parameters as voids play a critical role in the evolution of large scale structure.