PhD Defence Malte Brinch

Principal supervisor

• Professor Thomas R. Greve, DTU Space

Co-supervisors

• Associate Professor Georgios Magdis

Examiners

• Professor Lars Astrup Buchhave, DTU Space
• Professor Nina Hatch, University of Nottingham, UK
• Senior Researcher Helmut Dannerbauer, Instituto de Astrofísica de Canarias, Spain

Chairperson at defence

• Associate Professor Jérôme Chenevez

Summary

Galaxy clusters are the most massive virialized structures in the present day Universe, containing thousands of galaxies. Since the dawn of the concept of galaxies, astronomers have been studying the distribution of galaxies across the sky and found them to be non-symmetrical, with certain parts having high concentrations of galaxies in close proximity. To understand the formation and evolution of galaxy clusters, it is necessary to investigate their progenitors, the so-called protoclusters that inhabit the early Universe, since information pertaining to their evolution is lost as part of the virilization process. To study protoclusters, they must first be located, which is done through a number of different methods utilizing multi-wavelength data from the ultraviolet to the radio parts of the electromagnetic spectrum. Observers face challenges when it comes to locating protoclusters, as sufficient data over a large area is needed to distinguish the over dense protocluster from the field environment. Spectroscopic follow-up is often required to determine the systemic redshift of the protocluster,as many protoclusters are initially identified as over densities of photometrically selected galaxies. In this thesis, I go through the history and development of galaxy cluster studies and their progenitors, galaxy protoclusters. I explain the observational and theoretical advancements that have led to our current understanding of protoclusters. Next, I present my first paper which goes into how to locate and study protocluster candidates using large-scale photometric survey data in the COSMOS field. This work contributes to our current understanding of protoclusters by comparing them with our currently accepted models for protocluster evolution. The candidates can be used by the community as prime targets for follow-up studies by current and future instruments. My second paper presents a spectroscopic follow-up of one of the protocluster candidates I located in the COSMOS field. By utilizing the DEIMOS instrument on the Keck telescope, I search for detections of the Lyman-α emission line, which can be used to determine spectroscopic redshifts to the protocluster candidate galaxies. This contributes to the small sample of high redshift protocluster that has currently been observed. Lastly, I present my work on a compact galaxy group, which has detections of multiple lines in both emission and absorption and the continuum emission from ALMA.