Spectroscopic and structural properties of galaxies in a cluster environment 5.3 billion years ago

Abstract

We study how environment affects the structural and spectroscopic properties of galaxies in a massive merging cluster at &zeta; = 0.53. We obtain follow up spectroscopic observations of the cluster, originally identified in the HectoMAP survey, and confirm an additional 25 galaxies as cluster members (increasing cluster membership by 78%). We calculate <em>D&eta;</em>4000, a proxy for galaxy stellar population age, for all cluster members. We perform a statistical correction using photometric cluster member candidates to account for missing spectroscopic members. We analyze the <em>D&eta;</em>4000 - clustercentric distance relation of the cluster and find that galaxies at all clustercentric distances have similarly aged stellar populations, implying a mixture of star forming and quiescent galaxies at all cluster radii. Using available measurements, we examine the size-stellar mass relation to find that non-star-forming cluster members and member candidates with log₁₀(<em>M</em>_&lowast;/<em>M</em>_⊙) &gt; 10.5 are, on average, larger in the cluster environment than in the field.