TOPOLOGY IN GALAXY DISTRIBUTIONS - METHOD FOR A MULTISCALE ANALYSIS -A USE OF THE WAVELET TRANSFORM

We report the 2D analysis of distributions of galaxies in a search for structures on all scales, from groups up to superclusters (including the identification of voids), based on the use of the wavelet transfor m. The wavelet method is an objective, multi-scale technique which giv es the position, dimension and probability for each individual feature (both structures and voids) detected. We are currently performing the analysis on data from the COSMOS/UKST Southern Sky Galaxy Catalogue. The subsample used in our investigation contains some 2.5 x 10(6) gala xies in an area of similar to 140 x 45 degrees around the South Galact ic Pole. This is the first search for multi-scale objects on such an e xtended database, allowing us to cover many related topics in present- day Cosmology: realisation of superclusters as large-scale entities in their own right (as opposed to being considered merely as regions of enhanced cluster numbers); improvement in the definition of clusters o f galaxies with a new approach to their general behaviour (distributio n, typical sizes, state of evolution, etc.); and the objective charact erisation of voids, which is exclusive to the wavelet method. In the p resent paper, we demonstrate the power of the technique by applying it to a selected field covering approximately 3000 deg(2) in the Grus-Sc ulptor region. In this area, we find 7 large scale structures (of more than 5 degrees in extent) and 26 structures of smaller scales (cluste r-sized down to 1 degree, or group-sized down to 0.5 degrees). Sixteen of these small scale aggregates are connected with the large scale st ructures while ten appear isolated in the field. All these features ar e significant, having high confidence levels for detection. Voids are also detected in this area, likewise with high significance levels.