Abstract

Over the last 6-7 billion years, mature galaxy clusters, characterized by massive quiescent galaxy populations residing in Mh > 10^14 M⊙ dark matter halos, have become ubiquitous features of the cosmic web. These clusters are preceded by a proto-cluster stage, which form at much earlier times in filamentary dark matter overdensities and later collapse into a central halo. Identifying and characterizing protoclusters between the epoch of reionization and cosmic noon, during which time they are expected to undergo periods of rapid star formation and evolution prior to gravitational collapse, remains in its nascent stages. With a heterogeneous mix of selection techniques, spectroscopic completeness, area coverage, and wavelength coverage, we are still vitally lacking a statistically complete catalog of protoclusters — and even more so a general understanding of their physical properties. This doctoral thesis addresses these questions twofold by: 1) using luminous z∼6 quasars as tracers of overdensities at multiple wavelengths, and 2) presenting a comprehensive X-ray to radio case study of a massive protocluster at z=2.5. In the first half of this talk, I will present results from ALMA and HST of a search for enhanced galaxy evolution near quasars in the form of rare dusty star-forming galaxies and Lyman-break galaxies. I will show that quasar environments show strong variance in over density signals along individual sightlines and wavelength regimes, with some showing clear filamentary structure and others indistinguishable from a blank field. In the second half, I will present a multiwavelength analysis of a collapsing core associated with the Hyperion protocluster at z=2.5. I evaluate possible evolutionary hypotheses on the basis of the morphology of the cold gas needed for future star formation, the spatial distribution of its member galaxies, and the existence of a marginal X-ray detection that all present a challenge to our cosmological understanding of virial collapse of clusters during this epoch.