Star-formation rates of high-redshift galaxy clusters

Abstract

In this thesis, we take the first step toward building a star-formation limited sample of z ∼ 0.8 cluster galaxies with the goal of understanding the physical processes that affect star formation within the cluster environment. We present Hα narrow-band imaging results for four z ∼ 0.8 clusters. We reach 3σ star-formation rate (SFR) limits of ≤ 0.3 h⁻²₁₀₀M(⊙) yr⁻¹, demonstrating that near-infrared, narrow-band imaging centered on the observed wavelength of Hα is a powerful technique for sampling the entire Halpha luminosity function even at relatively high redshifts where Halpha emission moves into the near-infrared. Comparison with optical spectroscopy reveals a significant population of galaxies with Halpha emission but no [OII] emission. The integrated SFR per cluster mass increases with increasing redshift, consistent with the Butcher-Oemler effect. We compare our cluster SFRs with a limited sample of coeval field galaxies and find that cluster galaxies have lower SFRs than their field counterparts. However, a larger sample of coeval field galaxies is needed to make a more conclusive comparison. We model cluster infall using the extended Press-Schecter approach where we assume that the integrated star formation is dominated by galaxies that have been accreted during the last gigayear. The results show reasonable agreement for four out of seven clusters but differ by more than a factor of two for the remaining three clusters. A larger sample of clusters at similar redshifts will provide a more complete census of cluster star-formation properties and will allow a cleaner comparison with our infall model. We will continue to build such a sample of z ∼ 0.8 clusters.