The presence of substructure in galaxy groups and clusters is believed to be a sign of recent galaxy accretion and can be used not only to probe the assembly history of these structures , but also the evolution of their member galaxies .
Using the Dressler-Shectman ( DS ) Test , we study substructure in a sample of intermediate redshift ( z \sim 0.4 ) galaxy groups from the Group Environment and Evolution Collaboration ( GEEC ) group catalog .
We find that 4 of the 15 rich GEEC groups , with an average velocity dispersion of \sim 525 km s ^ { -1 } , are identified as having significant substructure .
The identified regions of localized substructure lie on the group outskirts and in some cases appear to be infalling .
In a comparison of galaxy properties for the members of groups with and without substructure , we find that the groups with substructure have a significantly higher fraction of blue and star-forming galaxies and a parent colour distribution that resembles that of the field population rather than the overall group population .
In addition , we observe correlations between the detection of substructure and other dynamical measures , such as velocity distributions and velocity dispersion profiles .
Based on this analysis , we conclude that some galaxy groups contain significant substructure and that these groups have properties and galaxy populations that differ from groups with no detected substructure .
These results indicate that the substructure galaxies , which lie preferentially on the group outskirts and could be infalling , do not exhibit signs of environmental effects , since little or no star-formation quenching is observed in these systems .