On the largest scale, the Universe resembles a cosmic spiderweb. Most galaxies coexist in small groups within the threads of this web. At the nodes of the threads are enormous groups of galaxies... Show moreOn the largest scale, the Universe resembles a cosmic spiderweb. Most galaxies coexist in small groups within the threads of this web. At the nodes of the threads are enormous groups of galaxies forming the largest structures in the universe still held together by gravity: clusters of galaxies.Clusters of galaxies consist of thousands of galaxies, although the galaxies constitute only a few per cent of the total cluster mass. The majority of the (non-dark) mass of a cluster is in a hot and dilute gas that resides in the space between galaxies and is permeated by magnetic fields. Clusters grow by collisions with other clusters, shocking and heating the gas causing amplification of magnetic fields and acceleration of particles to near the speed of light. This makes clusters a source of radio synchrotron radiation.This thesis investigates the particle acceleration process and the magnetic fields of merging clusters using the LOFAR and VLA radio telescopes. The thesis presents, among other things, one of the few radio maps of clusters at ultra-low frequencies and examines clusters of lower mass than usual. Additionally, the thesis includes observations of a sample of over a hundred clusters to statistically determine the properties of the magnetic field in clusters in a novel way. Show less
With the rapidly growing number of extrasolar planets detected, we have firmly stepped into the era of detailed characterization. Diverse types of exoplanets such as gas giants on close-in orbits ... Show moreWith the rapidly growing number of extrasolar planets detected, we have firmly stepped into the era of detailed characterization. Diverse types of exoplanets such as gas giants on close-in orbits (hot Jupiters) and young massive giants on wide orbits (super Jupiters), with no analogs in the Solar System, pose challenges but also opportunities to our understanding of planet formation and evolution. Exoplanet atmospheres with imprints from their history open an important avenue to retrace the origin and evolution of planets. With high-dispersion spectroscopy, we can resolve atomic and molecular spectral features into unique forests of lines that serve as the fingerprints for identifying different species in planetary atmospheres. In this dissertation, I utilize this technique to explore atmospheric compositions, thermal structures, and dynamics of exoplanet atmospheres. I have discovered minor isotopologues in emission spectra of an exoplanet and a brown dwarf for the first time, pioneering the use of carbon isotopic ratios as potential tracers of planet formation. I have investigated the trend of atomic absorption strengths in a sample of ultra-hot Jupiters, which enables disentangling different dynamic regimes of highly-irradiated exoplanets. These works form the foundation to link spectroscopic observations to planet formation and evolution processes. Show less
Over the last three decades, the discovery of exoplanets has revealed the boundless variety of worlds beyond our own Solar System. Majority of planetary systems contain short-period planets that... Show moreOver the last three decades, the discovery of exoplanets has revealed the boundless variety of worlds beyond our own Solar System. Majority of planetary systems contain short-period planets that are larger than Earth but smaller than Neptune. For rocky planets, the strong irradiation causes the surface to melt, forming dayside oceans of molten silicates. These are known as lava worlds. From a theoretical standpoint, lava worlds are expected to outgas silicate-rich atmospheres, which can be characterised using spectroscopy techniques. Spectroscopy allows astronomers to single out a multitude of chemical species in exoplanets, and with the James Webb Space Telescope (JWST), it is now possible to characterise even rocky planets.To reinforce our understanding of distant worlds it is critical that we can reproduce the observed results using computational models. A variety approaches exist, however due to their flexibility and adaptability, using averaged 1-D models is prefered. The work in this thesis heavily focuses on using 1-D chemistry and radiative-transfer codes to simulate atmospheres of super-Earths and sub-Neptunes, including volatile and silicate-rich compositions. The main goal is to guide observers to potentially detectable species that would help us gain insight into many of the drawn assumptions. The research done indicates a multitude of detectable species such as HCN, CN, CO, SiO, and SiO2. Models also show that silicate atmospheres are plagued with deep temperature inversions, strongly affecting observability. Most of the presented results are especially applicable to low-resolution infrared spectroscopy for observations with JWST. Show less
High-angular-resolution observations of the circumstellar material have uncovered numerous and very diverse substructures in protoplanetary discs, raising the question of whether they are caused by... Show moreHigh-angular-resolution observations of the circumstellar material have uncovered numerous and very diverse substructures in protoplanetary discs, raising the question of whether they are caused by forming planets or other mechanisms. This dissertation focuses on interpreting gas substructures in discs in the context of disc winds and planet-disc interactions. A special focus is put on transition discs, which show dust (and gas) depleted inner regions and represent ideal laboratories to observe planet formation in action and test disc evolution models. Radiative transfer and hydrodynamical models are combined to investigate photoevaporative winds acting in discs in which volatile carbon is reduced. Compared to solar metallicity discs, photoevaporative winds are stronger in such carbon-depleted discs, resulting in higher mass-loss rates and profiles that extend to larger radii. This may explain more of the observed transition disc population. Furthermore, a large number of transition discs are analysed through CO ALMA observations in terms of substructures in the kinematics and brightness temperatures. In particular, two sources, CQ Tau and HD 100546, are studied in detail and the analysis reveals prominent spiral features in both discs. Together with other substructures, these point towards ongoing planet formation. Show less
The Sun and all the stars in the night sky reside in the Milky Way galaxy. In the at-rest reference frame of the Galaxy, typical stars travel with velocities of about 100-200 kilometres per second... Show moreThe Sun and all the stars in the night sky reside in the Milky Way galaxy. In the at-rest reference frame of the Galaxy, typical stars travel with velocities of about 100-200 kilometres per second. Some stars, however, can attain velocities of several hundred to several thousands of kilometres per second. Accelerating stars to such high velocities is only possible in very energetic scenarios, such as supernova explosions or dynamical interactions with a supermassive black hole. By studying these fast stars, we can improve our understanding of the violent and short-lived events that accelerate them. This dissertation uses simulated fast-star populations and compares them to real-life fast star populations. In doing so, it provides new constraints on the final stages of stellar evolution and on the stellar environment in the centre of the Galaxy. Show less
The origin and evolution of galaxies are closely linked to many different physical phenomena. Among them, the most important one is the environment they reside in. Isolated and cluster member... Show moreThe origin and evolution of galaxies are closely linked to many different physical phenomena. Among them, the most important one is the environment they reside in. Isolated and cluster member galaxies indeed are affected by different forces which affect their evolution. The main concern of this thesis is to understand such forces and how they are related to galaxy evolution. Therefore, this thesis covers various topics including black hole mass calculations, the black hole mass-stellar velocity dispersion relation, the nature of AGN emission in galaxy clusters and field galaxies, a detailed investigation of X-ray and optical galaxy overdensity phenomenon, and the dynamical processes in pre-merging galaxy clusters. Show less
Dark matter is one of the biggest mysteries of the Universe. Its properties cannot be explained with the known laws of physics and elementary particles. Yet, it is the most abundant form of matter... Show moreDark matter is one of the biggest mysteries of the Universe. Its properties cannot be explained with the known laws of physics and elementary particles. Yet, it is the most abundant form of matter in the Universe.Several dark-matter theories exist, including cold dark matter (CDM), self-interacting dark matter (SIDM), and fuzzy dark matter (FDM). These theories make different predictions for the density profiles of dark-matter haloes (cuspy or cored), depending on the nature (CDM, SIDM, FDM) and properties (self-interaction strength, FDM particle mass) of dark matter. These profiles can be determined from the stellar kinematics of the galaxies hosted by the haloes. Many massive dwarf galaxies show cored profiles. However, baryonic processes such as star formation may also induce cores.In this thesis, I test CDM, SIDM, and FDM using the faintest and most dark matter–dominated galaxies, ultra-faint dwarf galaxies (UFDs), which offer a new perspective on the cusp–core problem. The stellar kinematics of UFDs should not be significantly affected by baryonic processes. I find that UFDs have no detectable cores, implying that the cores of more massive dwarf galaxies are not caused by dark-matter physics. I can also exclude the previously promising particle masses ~10^-22 eV/c^2 for FDM. Show less
Water is all around us and is vital for all aspects of life. Studying the various compounds and life forms that inhabit natural waters lets us better understand the world around us.Remote sensing... Show moreWater is all around us and is vital for all aspects of life. Studying the various compounds and life forms that inhabit natural waters lets us better understand the world around us.Remote sensing enables global measurements with rapid response and high consistency. Citizen science provides new knowledge and greatly increases the scientific and social impact of research.In this thesis, we investigate several aspects of citizen science and remote sensing of water, with a focus on uncertainty and accessibility. We improve existing techniques and develop new methods to use smartphone cameras for accessible remote sensing of water. Show less
Stars like the sun are born in large molecular clouds existing from gas and dust. During the formation process, the chemical composition of the material can be altered drastically by the changing... Show moreStars like the sun are born in large molecular clouds existing from gas and dust. During the formation process, the chemical composition of the material can be altered drastically by the changing physical conditions. This thesis focuses on how molecules in young protostellar systems are inherited from molecular clouds. The emphasis lies on so-called complex organic molecules and accretion shocks.Based on observations of complex organic molecules, it can be suggested that the molecular composition of a protostellar disk is (partially) inherited from the molecular cloud. The abundance ratio between various molecules is remarkably constant in various protostellar systems, implying that they form under similar conditions in molecular clouds. Furthermore, absence of complex molecules in observations does not directly mean that they are absent in the protostellar system but rather that they are hidden from us.This thesis also focuses on accretion shocks at the boundary between infalling cloud and protostellar disk. Based on a comparison between detailed numerical simulations and observations it can be suggested that strong accretions are not always present in protostellar systems. In turn, this suggests that the chemical composition in protostellar disks can be directly inherited from the molecular cloud. Show less
Low-mass main-sequence stars like our Sun are continuous sources of outflowing hot magnetised plasma. In the case of the Sun, this is known as the solar wind, whereas for other stars they are... Show moreLow-mass main-sequence stars like our Sun are continuous sources of outflowing hot magnetised plasma. In the case of the Sun, this is known as the solar wind, whereas for other stars they are called stellar winds. These types of stars comprise 93% of all stars in our galaxy, and also host the bulk of all exoplanets discovered to date. Therefore, understanding their wind outflows and how they interact with the planets they host is crucial to assessing the long-term evolution of planetary atmospheres, which in turn determines their potential to support life as we know it. The interactions between stellar winds and planets can also produce signals which could be detected with current-generation telescopes.Current measurements of the winds of low-mass main-sequence stars are limited, and have only been successful in a handful of cases. However, by coupling state-of-the-art magnetohydrodynamic (MHD) models of stellar winds with observational constraints, 3-dimensional snapshots of the wind environments around planet-hosting stars can be obtained. In this thesis, I utilise such models to explore the winds of these stars, and predict the potentially-observable signatures that may arise from their interactions with orbiting planets. Show less
One of the most important puzzles in modern astrophysics is the nature of dark matter. Stellar streams, formed by tidal stripping of the stars from globular clusters or dwarf galaxies, behave as a... Show moreOne of the most important puzzles in modern astrophysics is the nature of dark matter. Stellar streams, formed by tidal stripping of the stars from globular clusters or dwarf galaxies, behave as a group of test particles allowing us to measure the Milky Way’s dark matter content and, therefore, offering us a key to understanding its nature. Open clusters, loosely bound groups of stars that move through the Galaxy together, are, in contrast, an important driver of stellar evolution research. This Thesis presents our studies of these Galactic substructures and the conclusions we can draw on the larger Universe and physics based on these local observations. In chapters 2 - 4, we apply a novel method to map the Milky Way’s dark matter content using stellar streams, taking care to understand the various possible contributors to the systematics. Chapter 5 is dedicated to the study of the Hyades open cluster. Show less
Three major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope. Their surveys... Show moreThree major cosmology-focused missions are planned for the next decade: the Euclid space telescope, the Vera C. Rubin Observatory in Chile, and the Nancy Grace Roman Space Telescope. Their surveys will detect billions of galaxies over more than a third of the celestial sphere and out to redshifts of z~2 to constrain the evolving matterdistribution using weak gravitational lensing. This thesis focusses on ways of disentangling the contribution of normal matter, baryons for cosmologists, from the measured weak lensing signal for cosmic shear analyses and galaxy cluster mass calibrations. Combining the predictions of computer-simulated universes, evolving billions of particles in time, with simplified models that reproduce the observeddistribution of hot gas inside clusters of galaxies, but that freely vary the amount of matter where no observations are available, we have quantified how strongly our ignorance of the relation between ordinary and dark matter will affect the analysis of the planned surveys. Additionally, we have studied how baryons affect cluster massdeterminations and we suggest a new analysis method for cluster abundance studies that is less sensitive to our lack of knowledge of the exact distribution of normal matter in the outskirts of galaxy clusters. Show less
The intracluster medium (ICM) is a hot, tenuous and X-ray emitting gas that pervades galaxy clusters. Meanwhile, extended synchrotron sources, i.e., radio relics and radio halos are frequently... Show moreThe intracluster medium (ICM) is a hot, tenuous and X-ray emitting gas that pervades galaxy clusters. Meanwhile, extended synchrotron sources, i.e., radio relics and radio halos are frequently observed in galaxy cluster, for which the two widely accepted particle acceleration are shock acceleration and turbulent acceleration, respectively. Both of these scenarios are due to ICM motions, which means that X-ray observations of the ICM are fundamental for quantifying shock wave and turbulence properties to test the acceleration models. This thesis focuses on X-ray observations of galaxy clusters, and covers topics from ICM shock - radio relic connection to turbulence - radio halo connection. The new observational evidences further support the two acceleration scenario. Show less
I have studied the hot, diffuse gas around and between galaxies. Specifically, I have used the EAGLE numerical simulations of galaxy formation to predict the properties of this gas, and I have used... Show moreI have studied the hot, diffuse gas around and between galaxies. Specifically, I have used the EAGLE numerical simulations of galaxy formation to predict the properties of this gas, and I have used those properties to predict specific observables: soft X-ray absorption and emission lines. Measuring this gas is challenging, but if we can observe and characterise it, we can learn much about the gas flows in and out of galaxies that regulate their formation and evolution. Observations of soft X-ray lines with future X-ray telescopes, such as Athena and XRISM, will enable us to do so. For these future X-ray telescopes, the strongest X-ray absorption lines and essentially all detectable line emission will come from the gaseous haloes surrounding galaxies. Some weaker, but still detectable absorption lines will come from the more diffuse gas outside these haloes. Photo-ionisation by the intergalactic ultraviolet/X-ray radiation background affects the absorption and emission lines of the very diffuse gas between galaxies, and the diffuse edges of the galaxy haloes. Emission from this photo-ionised gas is not expected to be detectable, but some absorption should be. Show less
At the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The... Show moreAt the largest scales, two ingredients dictate the distribution of matter in the Universe. The first is dark matter, acting as an invisible scaffolding held together by gravitational forces. The second is dark energy, an enigmatic component responsible for the accelerated expansion of the Universe. Under these two forces, matter in the Universe organizes itself in the so-called cosmic web. The nodes of this network are large dark matter haloes, and this thesis explores how their boundaries provide information about the nature of dark energy and cosmology. Chapters 3 and 4 present robust theoretical predictions for this titular edge and discuss its simple physical interpretation. Chapters 2 and 5 corroborate these results by presenting measurements of this feature in weak-lensing data. The last scientific chapter of this thesis is a collection of studies in gravitational-wave physics. This chapter explores how these spacetime ripples observed from across the cosmos can be used to detect alternative theories of gravity. Show less
This thesis is an experimental study of the UV irradiation of the interstellar ice analogues, relevant for the different stages of the star and planet formation sequence. It describes in detail... Show moreThis thesis is an experimental study of the UV irradiation of the interstellar ice analogues, relevant for the different stages of the star and planet formation sequence. It describes in detail photodesorption and photoconversion processes, and as such, contributes to worldwide efforts that aim at understanding how chemistry in space could have contributed to the origin of life on Earth and possibly planets around other stars. Show less
In astronomy, the interpration of observations and measurements plays a crucial role: we rely purely and fundamentally on the information that reaches us as observers. And 80% of all matter in the... Show moreIn astronomy, the interpration of observations and measurements plays a crucial role: we rely purely and fundamentally on the information that reaches us as observers. And 80% of all matter in the universe is undetectable directly.This so called 'dark matter' can be observed indirectly, by the gravitational effect on its surroundings and the curvature of spacetime predicted by the theory of relativity.In this thesis, we combine scientific research, a description of our universe, with theoretical considerations of the statistical methods used for that research, or how we can deduce that description from the 'reflections' that we see. In this work, we focus on the matter distribution in groups and clusters of galaxies, and consider the intricacies of the method of weak gravitational lensing that we use, respectively. Show less
This thesis takes steps toward understanding the interaction between gas-phase and solid-state molecules in star- and planet-forming regions. Chapter 1 and 2 provide the reader with an introduction... Show moreThis thesis takes steps toward understanding the interaction between gas-phase and solid-state molecules in star- and planet-forming regions. Chapter 1 and 2 provide the reader with an introduction and in-depth description of methods used in subsequent chapters. Chapter 3 and 4 present the spectroscopic infrared characterization of acetaldehyde, dimethyl ether, ethanol, and methyl formate in the solid state, both pure and mixed in astronomically relevant matrices. This characterization will allow for probing of the solid-state organic inventory of star- and planet-forming regions with the upcoming James Webb Space Telescope. Interferometric observations of the protoplanetary disk around TW Hya with the Atacama Large Millimeter/submillimeter Array are presented in Chapter 5. These results hint that the observed gas-phase formaldehyde is formed in the gas phase, contrary to the generally accepted solid-state formation. Chapter 6 provides an insight to the interaction between gas-phase carbon monoxide and solid-state hydroxyl radicals on the surface of vacuum-UV irradiated water ice. Even tough residence times of carbon monoxide are short, they are sufficient to allow reactions with hydroxyl radicals and produce carbon dioxide. This process could explain the lack of gas-phase carbon monoxide in protoplanetary disks and the presence of carbon dioxide mixed in solid-state water. Show less
Galaxies form and live inside dark matter haloes. As a consequence, they are exposed to the tidal fields generated by the surrounding matter distribution: this imprints a preferential direction to... Show moreGalaxies form and live inside dark matter haloes. As a consequence, they are exposed to the tidal fields generated by the surrounding matter distribution: this imprints a preferential direction to the galaxy shapes, which leads to a coherent alignment on physically close galaxies, called intrinsic alignment. Intrinsic alignment is an important contaminant to weak lensing, which instead uses the correlation of galaxy shapes caused by the lensing effect of the matter distribution along the line of sight to infer the amount and the distribution of matter in the Universe.This dissertation studies the dependence of intrinsic alignment on galaxy properties such as luminosity, redshift and halo mass, using different techniques to measure it. It presents a model to account for the scale and sample dependence of the intrinsic alignment signal when modelling it in weak lensing studies. It also investigates the amount of biasing that incorrect modelling of intrinsic alignment would induce in the inferred cosmological parameters for ongoing and future surveys. The potential of weak lensing magnification is also explored to help constrain the cosmological parameters in upcoming surveys. Show less
One of the key quests in astronomy is to study the growth and evolution of galaxies across cosmic time. Radio observations provide a powerful means of studying the formation of stars and subsequent... Show moreOne of the key quests in astronomy is to study the growth and evolution of galaxies across cosmic time. Radio observations provide a powerful means of studying the formation of stars and subsequent buildup of distant galaxies, in a way that is unbiased by the presence of dust. This thesis provides a detailed view of faint, star-forming galaxies in the early Universe through sensitive radio observations, and compiles several studies probing distant star formation with both radio synchrotron and free-free emission. In Chapter 2, we detect a large number of galaxies using sensitive new radio data from the Very Large Array, allowing us to separate radio emission from star formation and active galactic nuclei in the faint radio sky. In Chapter 3, we calibrate synchrotron emission as a tracer of star formation in distant starburst galaxies, while in Chapters 4 & 5 we turn towards radio free-free emission — a faint but very powerful tracer of star formation. Using sensitive new radio data at high frequencies, we perform the first detailed studies of free-free emission in distant galaxies. Show less