The formation of blue cluster in local Universe

TL;DR

This study investigates the formation of blue galaxy clusters in the local universe, finding that recent accretion of blue satellites, rather than large-scale environment, primarily drives their development.

Contribution

It demonstrates that blue cluster formation is mainly due to recent accretion of blue satellites, challenging the idea that large-scale filamentary structures are the main cause.

Findings

Four blue clusters identified in SDSS data.

Blue clusters have later formation times.

Most blue satellites are recently accreted.

Abstract

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.