The realm of the galaxy protoclusters (1610.05201v2)

Abstract: The study of galaxy protoclusters is beginning to fill in unknown details of the important phase of the assembly of clusters and cluster galaxies. This review describes the current status of this field and highlights promising recent findings related to galaxy formation in the densest regions of the early universe. We discuss the main search techniques and the characteristic properties of protoclusters in observations and simulations, and show that protoclusters will have present-day masses similar to galaxy clusters when fully collapsed. We discuss the physical properties of galaxies in protoclusters, including (proto-)brightest cluster galaxies, and the forming red sequence. We highlight the fact that the most massive halos at high redshift are found in protoclusters, making these objects uniquely suited for testing important recent models of galaxy formation. We show that galaxies in protoclusters should be among the first galaxies at high redshift making the transition from a gas cooling regime dominated by cold streams to a regime dominated by hot intracluster gas, which could be tested observationally. We also discuss the possible connections between protoclusters and radio galaxies, quasars, and Ly-alpha blobs. Because of their early formation, large spatial sizes and high total star formation rates, protoclusters have also likely played a crucial role during the epoch of reionization, which can be tested with future experiments that will map the neutral and ionized cosmic web. Last, we review a number of promising observational projects that are expected to make significant impact in this growing, exciting field.

Essay on "The Realm of the Galaxy Protoclusters"

The paper "The realm of the galaxy protoclusters" by Roderik A. Overzier provides a comprehensive review of the current state of research on galaxy protoclusters, exploring their significance in the context of galactic and large-scale structure formation in the universe. The paper focuses on protoclusters—overdense regions of the early universe predicted to evolve into present-day galaxy clusters—and the role these primordial structures play in advancing our understanding of galaxy formation and evolution.

The paper of protoclusters is crucial as these structures offer insights into the early stages of cluster assembly, the evolution of cluster galaxies, and the environmental dependencies of galaxy evolution. Overzier reviews the primary techniques used to identify protoclusters, emphasizing both observational and simulation-based approaches. Observationally, protoclusters are detected through galaxy overdensities in surveys, employing methods such as the search for Lyman-break galaxies (LBGs), H$\alpha$ emitters (HAEs), and Ly$\alpha$ emitters (LAEs) within large-scale surveys. He also discusses the importance of simulations in providing estimates of present-day masses and the evolutionary trajectories of protoclusters.

The paper offers a detailed analysis of the characteristic features of protocluster galaxies. These features often include the presence of (proto-)Brightest Cluster Galaxies (BCGs), massive halos at high redshifts, and the early formation of the red sequence—a sequence of evolved, red, and passive galaxies typically found in galaxy clusters. It is noted that protoclusters provide an environment for testing recent models of galaxy formation, especially concerning the transition of galaxies from cold gas accretion-dominated regimes to those dominated by hot intracluster gas. Such transitions are hypothesized to occur earlier in protocluster environments than in the field, indicative of accelerated galaxy evolution in dense environments.

Overzier discusses how protoclusters may have significantly contributed to the cosmic reionization epoch given their large spatial scales, early formation, and high star-formation rates. The implications of these structures during reionization highlight the dynamic interplay between proto-galactic environments and the evolving intergalactic medium.

The paper also offers a forecast of upcoming observational projects anticipated to contribute significantly to the field. With advancements in instrumentation and survey techniques, the paper of protoclusters is expected to transition from niche explorations to mainstream astrophysical research, unlocking further details surrounding their role in large-scale cosmic structure formation and evolution.

In conclusion, Overzier’s review underscores the importance of protoclusters as laboratories for studying fundamental processes in cosmic evolution. As further observations and simulations refine our understanding, protoclusters will continue to illuminate the complexities of galaxy and structure formation throughout cosmic history, bridging theoretical predictions with empirical findings. The insights garnered from protoclusters are expected to advance significantly our understanding of both galaxy evolution and the formation of the large-scale structure of the universe. Future developments in observational technology, such as the James Webb Space Telescope, alongside enhanced simulation capabilities, present exciting opportunities to deepen our grasp on these formative cosmic structures.