A Three‐dimensional Wavelet Analysis of Substructure in the Coma Cluster: Statistics and Morphology

Abstract

Evidence of clustering within the Coma Cluster is found by means of a multiscale analysis of the combined angular-redshift distribution. We have compiled a catalog of 798 galaxy redshifts from published surveys of the region of the Coma Cluster. We examine the presence of substructure and of voids at different scales ranging from ~1 to ~16 h-1 Mpc, using subsamples of the catalog ranging from cz = 3000 km s-1 to cz = 28,000 km s-1. Our substructure detection method is based on the wavelet transform and on segmentation analysis. The wavelet transform allows us to find structures at different scales, and the segmentation method allows a quantitative statistical and morphological analysis of the sample. From the whole catalog, we select a subset of 320 galaxies, with redshifts between cz = 5858 km s-1 and cz = 8168 km s-1, which we identify as belonging to the central region of Coma and upon which we have performed a deeper analysis, on scales ranging from 180 h-1 kpc to 1.44 h-1 Mpc. Our results are expressed in terms of the number of structures or voids and their sphericity for different values of the threshold detection and at all the scales investigated. According to our analysis, there is strong evidence of multiple hierarchical substructure, on scales ranging from a few hundreds of kiloparsecs to about 4 h-1 Mpc. The morphology of these substructures is rather spherical. On a scale of 720 h-1 kpc we find two main subclusters that have been found before, but our wavelet analysis shows even more substructures, whose redshift position is approximately marked by the following bright galaxies: NGC 4934 and 4840, NGC 4889, NGC 4898 and 4864, NGC 4874 and 4839, NGC 4927, and NGC 4875.