2001A&A...378..408S

Result. of a systematic study of substructure in X-ray surface brightness distributions of a combined sample of 470 REFLEX+BCS clusters of galaxies are presented. The fully automated morphology analysis is based on data of the 3rd processing of the ROSAT All-Sky survey (RASS-3). After correction for several systematic effects, 52±7 percent of the REFLEX+BCS clusters are found to be substructured in metric apertures of 1Mpc radius (H₀=50km/s/Mpc). Future simulations will show statistically which mass spectrum of major and minor mergers contributes to this number. Another important result is the discovery of a substructure-density relation, analogous to the morphology-density relation for galaxies. Here, clusters with asymmetric or multi-modal X-ray surface brightness distributions are located preferentially in regions with higher cluster number densities. The substructure analysis techniques are used to compare the X-ray morphology of 53 clusters with radio halos and relics, and 22 cooling flow clusters with the REFLEX+BCS reference sample. After careful equalization of the different ``sensitivities'' of the subsamples to substructure detection it is found that the halo and relic sample tends to show more often multi-modal and elongated X-ray surface brightness distributions compared to the REFLEX+BCS reference sample. The cooling flow clusters show more often circular symmetric and unimodal distributions compared to the REFLEX+BCS and the halo/relic reference samples. Both findings further support the idea that radio halos and relics are triggered by merger events, and that pre-existing cooling flows might be disrupted by recent major mergers.