ar X iv : a st ro - p h / 96 10 05 6 v 1 9 O ct 1 99 6 Revealing Galaxy Associations in Abell 119

We report the results of an analysis of the hierarchical properties of the cluster of galaxies Abell 119. Observational data from the ESO Nearby Abell Cluster Survey (ENACS) are used, complemented by data from previous studies, while the analysis is performed with the S-tree method. The main physical system and its three subgroups with truncated Gaussian velocity distributions are identified; due to their remarkable physical features and possible cosmogonical mission we call these subgroups galaxy associations. The mass centre of the core of main system is shown to coincide with the X-ray centre of the cluster. An alignment of the mass centres of the 3 galaxy associations is also shown. The cluster of galaxies Abell 119 has attracted much attention, particularly due to its remarkable X-ray properties, known since Ariel-V measurements 1. Later observations by EXOSAT 2 allowed more detailed analysis of the physical conditions within the cluster, and, combined with photometric and spectroscopic data for the member galaxies , study of the substructuring properties of the cluster 3. The question of substructure of cluster of galaxies is critical to an understanding of the mechanisms of their formation, and numerous studies support the existence of subgroups in clusters (see, e.g., ref. 4). Below we reconsider the problem of the substructure of A119, based the ENACS data complemented with the data from ref. 3; this sample includes information on the redshifts, 2-D coordinates , and magnitudes of 142 galaxies. The ENACS dataset 5,6 contains redshifts for over 5000 galaxies in 107 southern-sky clusters selected from the Abell-Corwin-Olowin catalogue. The reliability and accuracy of the ENACS velocity measurements have been extensively discussed in the presentation of the survey (e.g., Fig. 4 in ref. 6). Specifically for A119, comparison has been made between