Joseph Cairns

At z > 2, many studies have identified protoclusters - overdensities of galaxies spanning tens of Mpc in size and hosting some of the most vigorous star formation observed in the Universe to date. Conversely, galaxy clusters are typically observed at z ~ 1 and are massive, virialised and abundant in quiescent, elliptical galaxies. Current models of galaxy formation and evolution predict that protoclusters will evolve into z ~ 0 massive galaxy clusters, and so there must be some rapid, environmentally-driven quenching of star formation at z ~ 1 that transforms protoclusters into clusters. In order to understand this evolution, we must search for overdensities of galaxies at the onset of cluster formation at which time we can observe the full web of activity: the assembly of a collapsed cluster core feeding on the star-forming filamentary material that resides in the protocluster web. In this project, we present an analysis of SpARCS J0330, one of the most massive, high-z galaxy clusters discovered to date. By building up SEDs with up to 20-band photometry for the spectroscopically confirmed cluster members, as well as for the potential cluster members, we aim to map out distant, star-forming galaxies over a ~15Mpc region across the cluster, bridging the gap between studies of high-z protoclusters and local galaxy clusters, and providing critical insights into how galaxy clusters form out of the cosmic web. We find that typically our cluster members reside below the main sequence, indicating that they have lower SFRs than expected for their stellar masses. We find that the SFR remains roughly constant with projected cluster centric distance within the core of the cluster, with SFRs typically lower than high redshift protoclusters, but higher than more local, massive galaxy clusters. There is, however, a shallow increase in SFR with projected cluster centric radius towards the outskirts of the cluster. We also see some evidence of substructure within the core of the galaxy cluster. These preliminary results indicate that the environmental quenching of galaxy clusters may have already begun by z ~ 1.6.