Within the field of astronomy, understanding how galaxies grow and evolve from the Big Bang to the present day is a challenging and complex question. Radio observations - unhindered by dust... Show moreWithin the field of astronomy, understanding how galaxies grow and evolve from the Big Bang to the present day is a challenging and complex question. Radio observations - unhindered by dust attenuation - are a powerful tool in studying the formation of stars and subsequent buildup of galaxies. In this thesis, the distant star formation is studied using radio observations from the VLA COSMOS-XS survey specifically. In Chapter 2, we discuss the details of the sensitive COSMOS-XS survey and present the derived Euclidean-normalized source counts. In Chapter 3, we derive the dust-unbiased star formation rate density out to high redshift and present evidence for a significant underestimation of the star formation rate density based on ultraviolet observations. In Chapter 4, the focus shifts to the ‘optically dark’ population: extremely dust-obscured sources that are invisible even in deep ultraviolet imaging. We identify these sources with the COSMOS-XS survey and use them to quantify their contribution to the total star formation rate density. In Chapter 5, we present new ALMA observations of ‘optically dark’ sources and confirm the cosmic importance of ‘optically dark’ sources at high redshift. Show less
Galaxies in the Universe are distributed along the intricate framework of the Cosmic Web. Groups and clusters of galaxies comprise the densest regions in this network, and therefore, are excellent... Show moreGalaxies in the Universe are distributed along the intricate framework of the Cosmic Web. Groups and clusters of galaxies comprise the densest regions in this network, and therefore, are excellent cosmic laboratories to study different aspects of galaxy evolution in extreme environments. In this thesis, we explore a wide range of properties of cluster galaxies and their host systems, such as the spatial distribution of mass in galaxies within clusters, the faint and diffuse stellar halo in groups and clusters, and processes that quench massive galaxies in high-redshift clusters. For this exploration, we develop methods to enable and optimise detailed comparisons of state-of-the-art observations and cosmological hydrodynamic simulations over more than half of the age of the Universe. Through our carefully-designed analyses, we test the validity of the simulations for studying the low-surface-brightness and high-redshift Universe. We also demonstrate how such comparisons can provide novel insights and motivate new tests for understanding galaxy evolution in dense environments. Show less
Outflows are crucially important for the gas budget and evolution of luminous star-forming galaxies and AGNs, with observed mass outflow rates of the same order as the star formation rate. Greater... Show moreOutflows are crucially important for the gas budget and evolution of luminous star-forming galaxies and AGNs, with observed mass outflow rates of the same order as the star formation rate. Greater star formation and black hole growth lead to more intense feedback and outflows, resulting in self-regulated galaxy growth. Multi-phase observations show that the cool molecular and atomic gas dominate the mass and momentum budget of massive galaxy outflows which additionally remove the direct fuel for star formation. In this thesis we target the molecular and atomic outflows at cosmic noon and dawn where the most extreme star formation and black hole activity is found but where current observations are severely lacking. Techniques commonly used to detect outflows in the nearby universe with emission lines are, however, challenging or impossible with current technology at the high-redshifts of this thesis. Molecular absorption lines provide a powerful and reliable alternative which is demonstrated with the OH+ and OH molecules in this thesis. With observations from the Atacama Large Millimeter/submillimeter Array (ALMA), this thesis provides cutting-edge comparisons of molecular/neutral outflows at cosmic dawn/noon between star-forming galaxies and dusty quasar hosts. Show less
Understanding how galaxies form in our dark matter dominated Universe is a key goal of extragalactic astronomy. Both the stellar mass function and the spatial distribution of galaxies provide... Show moreUnderstanding how galaxies form in our dark matter dominated Universe is a key goal of extragalactic astronomy. Both the stellar mass function and the spatial distribution of galaxies provide insights in the connection between dark matter and the stellar component. This thesis presents measurements on the stellar component in the most massive structures formed in the Universe, with the potential to test and further expand current physical models and thus our understanding of the cosmos. After studying 10 clusters in the distant Universe (Chapter 2-4), and 10 clusters in the local Universe (Chapter 5), we consider different evolutionary scenarios to explain the observed trends. Chapter 6 presents measurements on the very distant Universe, probing a time at which these massive structures have not yet formed. Show less
Galaxies have changed drastically over the past 10 billion years. This thesis deals with these changes, focusing on evolution in the structure of very massive galaxies with a range of stellar... Show moreGalaxies have changed drastically over the past 10 billion years. This thesis deals with these changes, focusing on evolution in the structure of very massive galaxies with a range of stellar population properties. The main subjects addressed are the rapid changes in the sizes of old galaxies, the gradients in stellar population content within galaxies, and the predictions from theoretical models regarding these properties. Show less
Galaxies with all their varieties, have been home to billions of stars during their life. It is because of the presence of these shining stars that we are able to observe them through the cosmic... Show moreGalaxies with all their varieties, have been home to billions of stars during their life. It is because of the presence of these shining stars that we are able to observe them through the cosmic time. Although we observe galaxies mostly through the light emitted by their stars, we cannot resolve these stars individually unless they are very close by. Because of this, the cumulative light from billions of stars in every galaxy is analyzed using stellar population models to extract information about the evolution of galaxies. Stellar light does not reach us without passing through the interstellar medium (ISM) which contains clouds of gas and dust particles. Gas and dust can absorb and re-emit the light from stars, or scatter it towards us and make interpreting what we observe in galaxies very complicated. Despite all these difficulties, just by analyzing the total light from galaxies, we can constrain the global physical properties of galaxies such as stellar mass, star formation rate and age, based on the stellar population models. By combining stellar population models and photoionization models we can further analyze the emission line spectrum of star-forming galaxies coming from ionized gas around young stars which provide us with a wealth of information about the small-scale properties of galaxies e.g., the ISM. This thesis is an attempt in understanding the relation between these small-scale properties and global properties of star-forming galaxies over cosmic time using stellar population synthesis models and photoionization models. Show less
One of the important properties of galaxies is their sizes which correlate with their stellar masses. Evidence is provided by many recent studies that the sizes of galaxies were smaller at higher... Show moreOne of the important properties of galaxies is their sizes which correlate with their stellar masses. Evidence is provided by many recent studies that the sizes of galaxies were smaller at higher redshifts compared to galaxies of similar mass in the local Universe. It is essential to understand which physical processes could explain the evolution of galaxy properties and the growth of the galaxies with time. Among different proposed scenarios, each mechanism could affect differently on the growth of stellar mass and hence sizes of galaxies. Consequently, determining these properties is essential to constrain the plausible model(s) for describing galaxy evolution. In this thesis, I will present the study of the mass-size evolution of galaxies from z=7 to z=1. I will also present the stellar mass-size relation for nearby galaxies (z=0), for samples selected using different criteria down to the stellar mass of 10^{9} solar mass. The robustness of size measurement techniques for z=0 and z=1 galaxies is also studied in details. Show less
