Results 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 automized 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 \pm 7 percent of the REFLEX + BCS clusters are found to be substructured in metric apertures of 1 Mpc radius ( H _ { 0 } = 50 { km } { s } ^ { -1 } { Mpc } ^ { -1 } ) .
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 analyses 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 .