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
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
This dissertation presents a new perspective on the life, work and character of the Dutch physical chemist Jacobus Henricus van ’t Hoff, first recipient of the Nobel Prize in Chemistry, and one of... Show moreThis dissertation presents a new perspective on the life, work and character of the Dutch physical chemist Jacobus Henricus van ’t Hoff, first recipient of the Nobel Prize in Chemistry, and one of the most important and colourful scientists in Dutch history. The image of Van ’t Hoff that emerges from the research presented in this dissertation is that of someone with a strong drive to make a name in science, who nonetheless always remained an outsider. The only major biography was already published in 1912, and was rather uncritical, if not heroizing. Therefore, it was high time for a new one, covering all insights gained over the past hundred years into his scientific research, his personal life and their mutual influence. Public and family archives have delivered a wealth of previously unknown (personal) documents, letters, diaries etc. which to a large extent had never been studied before. They offer previously unknown insights into the character of Van ‘t Hoff and shed new light on the interaction between the personality and scientific work of this leading chemist of the nineteenth century. Apart from these biographical aspects the biography also covers more general historical issues like the internationalisation of science at the end of the nineteenth century, the founding of the new discipline of physical chemistry in the same period, and the changing relationship between education and research in Dutch universities and abroad. Show less
Even though more than 4000 extra-solar planets are known today, only a small fraction of these has been captured in an image. To better understand the planet formation mechanisms in solar-like... Show moreEven though more than 4000 extra-solar planets are known today, only a small fraction of these has been captured in an image. To better understand the planet formation mechanisms in solar-like environments we started the Young Suns Exoplanet Survey (YSES). YSES targets a homogeneous sample of seventy young (~15Myr), Sun-like stars of the Scorpius-Centaurus association to search for sub-stellar companions. High-contrast imaging observations that were collected with the SPHERE instrument at the Very Large Telescope revealed (i) a shadowed transition disk around Wray 15-788 that shows significant signs of ongoing planet formation and (ii) one of the lowest-mass companions imaged to date: YSES 2b has a mass of 6.5 Jupiter masses and is orbiting its solar-mass primary at a separation of 110 au. Most intriguing, though, was (iii) the discovery of the first directly imaged multi-planet system around a Sun-like star. The detection of two gas-giant companions of 14±3 and 6±1 Jupiter masses that are orbiting YSES 1 at separations of 160 au and 320 au, respectively, provides important implications for the outer architecture of planetary systems and the underlying formation mechanisms. Show less
Organic molecules in interstellar space are important as they influence the structure of galaxies and star formations. Studying catalytic processes in space allows us to understand how molecular... Show moreOrganic molecules in interstellar space are important as they influence the structure of galaxies and star formations. Studying catalytic processes in space allows us to understand how molecular species are formed and chemically evolved in the interstellar medium and solar system objects. Quantum chemical methods, such as “Density Functional Theory” (DFT), can be employed to study the chemical pathways for the formation of molecular species, which is challenging with only observations and experiments. This thesis studies, with DFT methods, how polycyclic aromatic hydrocarbons (PAHs), the most abundant organic species in space, catalyze the formation of molecular hydrogen in the interstellar medium. Specifically, how linear PAHs become superhydrogenated and how the presence of Stone Wales defect in PAHs contributes to their catalytic activity for molecular hydrogen formation. In addition, this thesis reports the study of the catalytic activity of forsterite, a silicate mineral abundant in grains, asteroids, and meteorites. Specifically, the presence of Schottky MgO vacancy in forsterite can catalyze the C-H activation of PAHs as the first step to study the breakdown reaction of PAHs in asteroidal settings. The latter is indispensable to understand the formation of the so-called organic inventory of solar system objects. Show less
In this thesis, I studied the origin and evolution of the non-thermal radiation in merging galaxy clusters. Cluster mergers are the among the most energetic events in the Universe. Part of this... Show moreIn this thesis, I studied the origin and evolution of the non-thermal radiation in merging galaxy clusters. Cluster mergers are the among the most energetic events in the Universe. Part of this energy is released in turbulence and shock waves which can (re-)accelerate cosmic rays and amplify magnetic fields in the intra-cluster medium (ICM). The interaction of these results in large-scale synchrotron radiation, which is visible through radio observations. In addition, X-ray observations of the ICM were carried out to investigate the dynamical state of the clusters, and the properties of cluster shocks. Show less
This thesis aims to demonstrate how the achromatic nature and design flexibility of liquid-crystal optics can be used to improve high-contrast imaging instruments to facilitate detailed exoplanet... Show moreThis thesis aims to demonstrate how the achromatic nature and design flexibility of liquid-crystal optics can be used to improve high-contrast imaging instruments to facilitate detailed exoplanet characterization.Chapter 2 discusses the design, performance, and future development of the liquid-crystal vector-apodizing phase plate (vAPP) coronagraph, five of which have been installed in different instruments on current generation telescopes since 2016. In chapter 3 we use the achromatic nature of the vAPP in combination with the LBT/ALES integral field spectrograph to obtain the first ever thermal infrared spectrum of the inner three HR 8799 planets. In Chapter 4 and 8 we show that by combining multiple grating patterns to reduce the influence of polarization leakage, we can improve the performance of liquid-crystal coronagraphs. In Chapter 5 and 6 we enhance sparse aperture masking, capable of detecting companions beyond the diffraction limit, by using liquid-crystal phase masks to enable low-resolution spectroscopy and improve throughput. In Chapter 7 we demonstrate that a liquid-crystal Zernike wavefront sensor can accurately and efficiently measure phase and amplitude aberrations simultaneously, facilitating extreme contrasts. Together, the concepts presented in this thesis can be used to improve high-contrast imaging instruments of both ground-based and space-based observatories. Show less
The thesis deals with the study of giant radio galaxies (GRGs), which are radio galaxies of megaparsec sizes. Their enormous size and rarity have been investigated in this thesis. The study... Show moreThe thesis deals with the study of giant radio galaxies (GRGs), which are radio galaxies of megaparsec sizes. Their enormous size and rarity have been investigated in this thesis. The study included searching and consequent finding of the largest samples of GRGs and thereby enabling to study of their properties in detail. Also, the properties were compared to smaller sized radio galaxies to investigate possible differences which could be the factor for their giant sizes. Show less
The origin and evolution of galaxies are closely tied to the cyclic feedback processes between stars and the interstellar medium (ISM). The aim of this thesis is to explore characteristics of the... Show moreThe origin and evolution of galaxies are closely tied to the cyclic feedback processes between stars and the interstellar medium (ISM). The aim of this thesis is to explore characteristics of the ISM, on global (galactic) scales down to sub-cloud (pc) scales. We explore new methods to investigate the ISM in external galaxies, through radio recombination line observations, and develop the tools and strategies needed to process new low-frequency observations with the Low Frequency Array. We also infer the presence of massive stars and characterize their properties and influence on the ISM. This thesis addresses the questions:- How does low-density ionized gas affect the evolution of the massive, galactic star-forming region, Cygnus X? Are the same fingerprints present in surveys of low-density ionized gas in our Galaxy?- What are the properties of star formation (star clusters) in the central starburst of the galaxy NGC 4945?- Can the ISM be explored outside of the local universe through radio recombination line observations? What are the ISM properties of a dwarf-like galaxy at z=1.1?- What techniques are best suited to detect faint radio recombination lines (at a previously unknown redshift) in extragalactic sources? Show less
Circumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available... Show moreCircumstellar discs are the reservoirs of gas and dust that surround young stars and have the potential to become planetary systems. Their evolution will determine the time and material available to form planets. Studying the evolution of circumstellar discs can then help us understand planet formation and the diversity of observed planetary systems. These discs develop almost immediately after star formation, as a direct consequence of the collapse of a molecular cloud and angular momentum conservation. Their surroundings are rich in gas and neighbouring stars, which can be hostile to the discs and affect their evolution in different ways: dynamical encounters with nearby stars can truncate the discs; stellar winds and supernovae explosions can truncate, tilt, or completely destroy the discs; and the presence of bright, massive stars in the vicinity of circumstellar discs can heat their surface enough to evaporate mass from them. This process, known as external photoevaporation, is arguably one of the most important environmental mechanisms in depleting mass from young circumstellar discs. The work performed for this thesis consisted of simulating the early evolution of circumstellar discs in star clusters and the effects of the environment, in particular, truncations due to close encounters and photoevaporation. The results show that photoevaporation is extremely efficient in removing mass from the discs, greatly limiting the amount of material and time available to form planets. Show less
