The formation of blue cluster in local Universe
  It is well known from the Butcher-Oemler effect that galaxies in dense
environment are mostly red with little star formation and the fraction of blue
galaxies in galaxy groups/clusters also declines rapidly with redshifts. A
recent work by Hashimoto et al. reported a local 'blue cluster' with high
fraction of blue galaxies ($\sim 0.57$), higher than the model predictions.
They ascribed this blue cluster to the feeding of gas along a filamentary
structure around the cluster. In this work we use group catalog from the Sloan
Digital Sky Survey Data Release 7 (SDSS DR7) and the state-of-art of
semi-analytic model (SAM) to investigate the formation of blue clusters in
local Universe. In total, we find four blue clusters with halo mass $\sim
10^{14}M_{\odot}$ at $0.02 < z < 0.082$, while only the one found by Hashimoto
et al. is in a filamentary structure. The SAM predicts that blue clusters have
later formation time and most blue satellite galaxies are recently accreted. We
conclude that the formation of blue clusters is mainly governed by newly
accreted blue satellites, rather than the effect of large-scale environment.
