The realm of the galaxy protoclusters

摘要

The study of galaxy protoclusters is beginning to fill in unknown details ofthe important phase of the assembly of clusters and cluster galaxies. Thisreview describes the current status of this field and highlights promisingrecent findings related to galaxy formation in the densest regions of the earlyuniverse. We discuss the main search techniques and the characteristicproperties of protoclusters in observations and simulations, and show thatprotoclusters will have present-day masses similar to galaxy clusters whenfully collapsed. We discuss the physical properties of galaxies inprotoclusters, including (proto-)brightest cluster galaxies, and the formingred sequence. We highlight the fact that the most massive halos at highredshift are found in protoclusters, making these objects uniquely suited fortesting important recent models of galaxy formation. We show that galaxies inprotoclusters should be among the first galaxies at high redshift making thetransition from a gas cooling regime dominated by cold streams to a regimedominated by hot intracluster gas, which could be tested observationally. Wealso discuss the possible connections between protoclusters and radio galaxies,quasars, and Ly-alpha blobs. Because of their early formation, large spatialsizes and high total star formation rates, protoclusters have also likelyplayed a crucial role during the epoch of reionization, which can be testedwith future experiments that will map the neutral and ionized cosmic web. Last,we review a number of promising observational projects that are expected tomake significant impact in this growing, exciting field.