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
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
Complex Organic Molecules (COMs) have been detected in objects across different stages of stellar evolution. Many of these COMs are expected to form on interstellar ice and transfer later to the... Show moreComplex Organic Molecules (COMs) have been detected in objects across different stages of stellar evolution. Many of these COMs are expected to form on interstellar ice and transfer later to the gas phase. However, due to the challenge of detecting and assigning molecules in interstellar ice observations, the only frozen COM that has been unambiguously identified is methanol. This scenario is about to change, as the exceptional capabilities of the James Webb Space Telescope (JWST) enable the observation of weak signatures of molecules in interstellar ice.This thesis has a main focus on laboratory studies to support interstellar ice observation with the JWST. The results of the spectroscopic characterization of three COMs, acetone, methylamine, and methyl cyanide mixed in interstellar ice analogs are presented in Chapters 3, 4, and 5, respectively. The potential of their absorption features to trace these species in JWST observations is also discussed. Chapter 6 presents a new experimental approach to studying morphological changes in frozen CO, which is important to understand its morphology in space. Chapter 7 presents a computational study that simulates the infrared spectra of small fullerenes (between 44-70 C atoms) and provides insights for future JWST searches for these molecules 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
This thesis focus on the interaction between M dwarf stellar winds and Galactic cosmic rays and the possible effects on the habitability of exoplanets. We use numerical simulations to describe the... Show moreThis thesis focus on the interaction between M dwarf stellar winds and Galactic cosmic rays and the possible effects on the habitability of exoplanets. We use numerical simulations to describe the stellar winds of M dwarfs using observable constraints, such as the mass-loss rate, X-ray luminosity, and magnetic field strength/flux. Additionally, we use numerical simulations to describe the propagation of Galactic cosmic rays within M dwarf planetary systems. With these simulations, we can calculate the flux of Galactic cosmic rays reaching exoplanet magnetospheres/atmospheres. Measuring cosmic ray fluxes in exoplanet atmospheres is yet not possible, but cosmic rays are an important ingredient in the context of planetary habitability. For this reason, quantifying these fluxes is essential to complete the habitability “puzzle”. Future exoplanet atmosphere observations with space telescopes, such as the JWST and the ARIEL, will enable us to constrain cosmic ray fluxes in exoplanet atmospheres. Show less
Until the 1990s, the only known planets were those in our Solar System. Three decades later, several thousand exoplanets have been discovered orbiting stars other than the Sun, and substantial... Show moreUntil the 1990s, the only known planets were those in our Solar System. Three decades later, several thousand exoplanets have been discovered orbiting stars other than the Sun, and substantial efforts have been made to explore these strange new worlds through spectroscopic analyses of their atmospheres. In particular, high-dispersion spectroscopy has provided robust measurements of these objects, enabling investigations of the significant, outstanding questions of exoplanetary science: What kinds of planets exist beyond our Solar System? Of what are they made? How did they form? Is there life beyond Earth? This dissertation touches upon all of these topics. Chapter 2 details a study to understand the chemical composition of one of the most extreme exoplanets. Chapter 3 investigates the feasibility of studying the different isotopes of titanium in large gaseous exoplanets, which may provide insight into their formation. Chapter 4 presents an attempt to detect young, still-forming planets in an effort to better understand how this process works. Chapter 5 concludes this dissertation with an evaluation of the ability of large future telescopes to detect molecular oxygen in Earth-like exoplanets, which may trace the presence of life. 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
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
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
This Thesis shows discoveries in non-linear astrochemical kinetics as well as a deeper analysis of dark clouds chemistry. It is concluded that autocatalysis in interstellar gas-phase chemistry... Show moreThis Thesis shows discoveries in non-linear astrochemical kinetics as well as a deeper analysis of dark clouds chemistry. It is concluded that autocatalysis in interstellar gas-phase chemistry leads to bistability but when coupled with the gas-grain exchange of key species, the system can show Hopf bifurcation and lead to the appearance of complex chemical oscillations. The results and discussion of the five chapters allow further understanding of the chemical evolution in a gas phase system and in a gas-grain environment, providing better predictions to compare with future observations. Show less
We have conducted a full spectral line survey of the 3-13 micron region of two massive protostars, AFGL 2591 and AFGL 2136, for the first time at high spectral resolution. Utilising SOFIA/EXES... Show moreWe have conducted a full spectral line survey of the 3-13 micron region of two massive protostars, AFGL 2591 and AFGL 2136, for the first time at high spectral resolution. Utilising SOFIA/EXES observations, combined with ground based observations from TEXES and iSHELL, many transitions of HCN, C2H2, NH3, CS, CO and H2O are observed, with all species observed to be in absorption. High temperatures (600 K) and abundances (1-10e-6 w.r.t H) of each species are derived. In this thesis, I will present the new insights into the physical conditions and chemical composition of the disks that these absorption lines probe. In particular, hundreds of ro-vibrational transitions of H2O are detected with EXES towards each object, and are linked to a disk wind in AFGL 2591. Column density variations of HCN and C2H2 in bands that probe the same lower level, across different wavelengths, are also discussed, supporting the location of this gas in the circumstellar disk of these protostars. Finally emission lines of HCN are discussed towards MonR2 IRS 3 and are consistent with an origin in a circumstellar disk, or also possibly an expanding shell of gas, supported by P-Cygni profiles of CO lines. Show less
