Understanding how galaxies form, interact, and evolve comes largely from comparing theory predictions with observational data. Numerical simulations of galaxies provide the most accurate approach... Show moreUnderstanding how galaxies form, interact, and evolve comes largely from comparing theory predictions with observational data. Numerical simulations of galaxies provide the most accurate approach to testing the theory, as they follow the non-linear evolution of gas and dark matter in great detail and incorporate numerous baryonic processes, among which are energy feedback from supernovae (SNe) and Active Galactic Nuclei (AGN). In this thesis, we show the results of the development of the new model COLIBRE for cosmological simulations of galaxy formation that include a cold interstellar medium. First, we present a new SN feedback recipe developed for COLIBRE, whereby SN energy is injected into the gas in thermal and kinetic forms, and the total energy and momentum of the system of gas and stars are exactly conserved. Second, we conduct a detailed comparison of different ways in which SN energy is distributed in the gas environment around young stellar populations. Third, by using our simulation setup originally developed to test COLIBRE’s SN feedback, we show that the radioactive isotope Fe60 that has been detected on Earth is likely of SN origin. Finally, we present the calibration of the SN and AGN feedback of the COLIBRE model using machine learning. Show less
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
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
Galaxies in the local Universe fall into two main categories of spirals and ellipticals. In this Thesis, we explore the structural evolution of galaxies into this bimodal distribution. To do so, we... Show moreGalaxies in the local Universe fall into two main categories of spirals and ellipticals. In this Thesis, we explore the structural evolution of galaxies into this bimodal distribution. To do so, we study galaxies in the context of the Fundamental Plane, the tight scaling relation between galaxy size, kinematics and luminosity, which connects the structural and stellar population properties of galaxies. This work is built on a combination of observational data and theoretical models. Large spectroscopic surveys are used to construct a representative sample of massive quiescent and star-forming galaxies across 8 Gyr of cosmic time. We hence show that there is strong variation and evolution in the mass-to-light ratios of galaxies, due to evolution in the stellar populations. However, surprisingly, all galaxies lie on a single mass Fundamental Plane, which does not evolve with time. Cosmological simulations are used to assess the structural properties that may underlie the observed mass Fundamental Plane. Based on the simulations, we propose that this relation may originate from a systematic variation in the central dark matter content within galaxies as a function of their size and mass. 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
Although we have a broad picture of how the universe has evolved from the Big Bang more than 13.7 billion years ago, the details of the formation and evolution of galaxies are still not well... Show moreAlthough we have a broad picture of how the universe has evolved from the Big Bang more than 13.7 billion years ago, the details of the formation and evolution of galaxies are still not well understood. Using a combination of optical and infrared observations called the SIMPLE survey, it is possible to picture galaxies at different stages in their evolution. It appears that the star formation rate per unit mass, the specific star formation rate, has been steadily decreasing for over the last 10 billion years. During this period it was always lower for the most massive galaxies but the rate of change does not seem to be a strong function of mass. Using the specific star formation rate, it is possible to determine the fraction of galaxies that are passively evolving. It appears that 30% of the most massive galaxies already formed the bulk of their stars 10 billion years ago and have been passively evolving at least since then. This measurement can be used as a constraint for models of galaxy evolution. A comparison between such a model and the SIMPLE observations, shows that the models can not predict the correct growth rate through star formation well enough yet. Show less
