Star Formation and Supercluster Environment of 107 Nearby Galaxy   Clusters
  We analyze the relationship between star formation (SF), substructure, and supercluster environment in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Previous works have investigated the relationships between SF and cluster substructure, and cluster substructure and supercluster environment, but definitive conclusions relating all three of these variables has remained elusive. We find an inverse relationship between cluster SF fraction (f_SF) and supercluster environment density, calculated using the galaxy luminosity density field at a smoothing length of 8 h^-1 Mpc (D8). The slope of f_SF vs. D8 is -0.008 +/- 0.002. The f_SF of clusters located in low-density large-scale environments, 0.244 +/- 0.011, is higher than for clusters located in high-density supercluster cores, 0.202 +/- 0.014. We also divide superclusters, according to their morphology, into filament- and spider-type systems. The inverse relationship between cluster f_SF and large-scale density is dominated by filament- rather than spider-type superclusters. In high-density cores of superclusters, we find a higher f_SF in spider-type superclusters, 0.229 +/- 0.016, than in filament-type superclusters, 0.166 +/- 0.019. Using principal component analysis, we confirm these results and the direct correlation between cluster substructure and SF. These results indicate that cluster SF is affected by both the dynamical age of the cluster (younger systems exhibit higher amounts of SF); the large-scale density of the supercluster environment (high-density core regions exhibit lower amounts of SF); and supercluster morphology (spider-type superclusters exhibit higher amounts of SF at high densities). 
S. A. Cohen, R. C. Hickox, G. A. Wegner, M. Einasto, J. Vennik
astro-ph.GA