Voids in the distribution of galaxies: an assessment of their significance and derivation of a void spectrum

We have developed an algorithm to search for nearly spherical regions which are devoid of bright galaxies. The presence of empty regions, or voids, is an intrinsic property of any spatial point data set. Some means must thus be found of distinguishing between voids which are simply the result of underdensities in the observational data, and voids which have been produced by some physical mechanism. We choose to assess the significance of our candidate voids by means of Monte Carlo simulations, using random catalogues which mimic the selection effects of the actual data set. The resultant list of more than 100 voids throughout the entire sky is then used to derive a spectrum of void sizes.