Star Formation and Relaxation in 379 Nearby Galaxy Clusters

TL;DR

This study analyzes 379 nearby galaxy clusters to explore how star formation activity correlates with the clusters' dynamical relaxation state, revealing higher star formation in less relaxed clusters.

Contribution

It provides a large-scale analysis linking star formation rates to cluster relaxation, confirming a weak inverse correlation with improved data validation.

Findings

Unrelaxed clusters have higher star formation fractions.

Star formation fraction increases as clusters become less relaxed.

Results align with previous studies on cluster evolution.

Abstract

We investigate the relationship between star formation (SF) and level of relaxation in a sample of 379 galaxy clusters at z < 0.2. We use data from the Sloan Digital Sky Survey to measure cluster membership and level of relaxation, and to select star-forming galaxies based on mid-infrared emission detected with the Wide-Field Infrared Survey Explorer. For galaxies with absolute magnitudes M_r < -19.5, we find an inverse correlation between SF fraction and cluster relaxation: as a cluster becomes less relaxed, its SF fraction increases. Furthermore, in general, the subtracted SF fraction in all unrelaxed clusters (0.117 +/- 0.003) is higher than that in all relaxed clusters (0.097 +/- 0.005). We verify the validity of our SF calculation methods and membership criteria through analysis of previous work. Our results agree with previous findings that a weak correlation exists between cluster SF and dynamical state, possibly because unrelaxed clusters are less evolved relative to relaxed clusters.