Of all the mass in our Universe, 80% is thought to consist of a hypothetical and invisible substance called dark matter (DM). So far, all observations of DM are based on its gravitational... Show moreOf all the mass in our Universe, 80% is thought to consist of a hypothetical and invisible substance called dark matter (DM). So far, all observations of DM are based on its gravitational interaction, either through the dynamics of normal (baryonic) matter or through the deflection of light. The latter approach, called ‘gravitational lensing’, is a unique way to probe the distribution of DM without making any assumptions on its dynamical state, and on scales larger than the extent of baryons. Using weak gravitational lensing with the Kilo-Degree Survey (KiDS), we first study the relation between galaxies and their dark matter halos on the scale of individual galaxies and galaxy groups. We then attempt to measure the effect of the local and large scale (cosmic web) density distribution on galaxies and halos, and we measure the interplay between galactic and DM structures at the scale of the cosmic web. Finally, we perform the first test of Verlinde’s theory of Emergent Gravity, all with the ultimate goal of gleaning some insight into the possible nature of the elusive ‘missing mass’. Show less
Planets are formed in disks of gas and dust around young stars. These planet-forming disks undergo several physical and chemical processes that can lead to planetary systems like our own. This... Show morePlanets are formed in disks of gas and dust around young stars. These planet-forming disks undergo several physical and chemical processes that can lead to planetary systems like our own. This thesis uses data of two well known planet-forming disks around TW Hya and HD 163296 taken with the Atacama Large (sub)Milimeter Array (ALMA) and the Herschel Space Telescope to study the spatial distribution of their dust and gas content. In particular, we aim to constrain the spatial distribution of the main oxygen- and nitrogen-bearing species in planet-forming disks and to explore the relationship between their physical features and the formation and chemistry of common molecular species. By analysing water and ammonia emission form the disk around TW Hya, we conclude that the location of oxygen- and nitrogen-bearing volatiles in planet-forming disks are set by grain evolution, in particular radial drift. In addition, we conclude that the spatial location of temperature-sensitive species trace substructures in the temperature profile of protoplanetary disks and therefore (indirectly) the impact of dust evolution process on its morphology. Show less
In this thesis chemical and physical processes in the ice mantles on interstellar dust grains are studied. With the Atacama Large Millimetre/submillimetre Array molecules of interest to the... Show moreIn this thesis chemical and physical processes in the ice mantles on interstellar dust grains are studied. With the Atacama Large Millimetre/submillimetre Array molecules of interest to the formation of bigger, life-bearing molecules are detected for the first time around the sun-like low-mass protostar IRAS 16293-2422. These detections give clues about the earliest conditions our solar system formed under and potentially how life on earth emerged. Laboratory studies investigate the formation of these complex species in a laboratory set-up mimicking the conditions on interstellar icy dust grains. In this ways formation routes for molecules with a so-called amide functional group are mapped. Show less
In this work the reconstruction of a tau neutrino signal in the KM3NeT detector is discussed. Tau neutrinos leave a two shower signature in the detector, which is a unique signature among all... Show moreIn this work the reconstruction of a tau neutrino signal in the KM3NeT detector is discussed. Tau neutrinos leave a two shower signature in the detector, which is a unique signature among all neutrino interactions. By identifying and reconstructing these tau signatures the KM3NeT detector will be able to distinguish all three neutrino flavors. In addition, cosmic tau neutrinos suffer significantly less from atmospheric backgrounds, makign them ideal messengers for cosmic events. The presented reconstruction is the first tau reconstruction for the KM3NeT detector and resulted in a total expected observation rate of half a tau event per year for one unit of the KM3NeT detector. Show less
We investigate the buildup of galaxies from various vantage points. The first two chapters focus on the stellar content of galaxies, especially the distribution of stellar masses at birth and... Show moreWe investigate the buildup of galaxies from various vantage points. The first two chapters focus on the stellar content of galaxies, especially the distribution of stellar masses at birth and potential variations therein in various galactic environments. We find that in some cases these inferred variations can be due to an underestimation of model and measurement errors. Furthermore, we infer the consequences of these proposed variations on the interpretation of galaxy properties and galaxy formation processes. Chapters 3 and 4 focus on the buildup of galaxies in time through mergers and in-situ star formation. We test and improve observational models that aim to trace galaxies though cosmic time, by applying them to cosmological hydrodynamical simulations, for which we have access to the full history and evolution of galaxies since the beginning of time. The fifth chapter focusses on the buildup of galaxy morphology. We follow the buildup of morphological components in a cosmological simulation, which leads us to conclude that galaxy formation is a three-phase process, consisting of an early, rather disorganised, phase, followed by a phase in which stars are formed primarily in an organised rotating disk, and ending in a late phase of merger-driven spheroid formation. Show less
Galaxies form and evolve through close interaction with their surroundings. As a result, the heavy elements ('metals') that are synthesized in stars, are found both inside and outside galaxies.... Show moreGalaxies form and evolve through close interaction with their surroundings. As a result, the heavy elements ('metals') that are synthesized in stars, are found both inside and outside galaxies. They trace the gas returned by stars, while providing information on the time-scales and physical conditions characterizing various stages of galaxy evolution through their elemental composition and ionization state. In this thesis, we explore what metals can tell us about galaxy formation. We complement theoretical work using the EAGLE simulations, where we focus on the galaxies as well as the surrounding medium, with an observational study of the low-redshift (z < 1) circumgalactic medium using the MUSE instrument on the VLT. Show less
Over the past years it has been discovered that the population of extra-solar planets is large and diverse. This fact feeds expectations for finding habitable Earth-like planets and potentially... Show moreOver the past years it has been discovered that the population of extra-solar planets is large and diverse. This fact feeds expectations for finding habitable Earth-like planets and potentially extra-terrestrial life. However without a reliable characterization, the fundamental nature of these planets would remain unknown after their initial discovery. This thesis focuses on the development of new spectroscopic observation and analysis methods to characterize planets after their discovery. The techniques presented in this thesis can be used in the future to detect the signs of life and habitability on Earth-like exoplanets that are expected to be discovered over the coming years. Show less
Multiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary... Show moreMultiple stars, that is two or more stars composing a gravitationally bound system, are common in the universe.They are the cause of many interesting phenomena, from supernovae and planetary nebulae, to binary black hole mergers. Observations of main sequence stars, young stars and forming protostars show that multiplicity is common, and that multiple stars are born. This thesis focuses on several of the open questions on the formation and evolution of multiple stars, namely when do rotationally supported disks form, the factors leading to fragmentation of the cloud core and the physico-chemical structure of multiple protostars. For this purpose, radio interferometric observations of dust continuum and molecular line emission, coupled with chemical and physical models are used to study several young, deeply embedded prototstars. The results of this thesis contribute useful pieces to the puzzle of multiple star formation, demonstrating that rotationally supported disks can form early in the star formation process, while temperature and the presence of disks can alter the physico-chemical protostellar structure. Furthermore, the results of this thesis indicate that mass, rather than temperature, could be an important factor in fragmentation of cloud cores, and the formation of multiple stars. Show less
When a star gets too close to a supermassive black hole, it is torn apart by strong tidal forces in a tidal disruption event (TDE). The stellar matter then fuels the compact object causing a... Show moreWhen a star gets too close to a supermassive black hole, it is torn apart by strong tidal forces in a tidal disruption event (TDE). The stellar matter then fuels the compact object causing a bright flare that is a unique probe of the majority of galactic nuclei, otherwise quiescent. For example, the black hole properties can be estimated from this signal. In my thesis, I used analytical and numerical methods to shed light on the TDE dynamics and associated emission, a required step to optimally exploit this powerful predictive potential. I carried out a numerical study of the accretion disc formation from the stellar debris. The results strongly challenged previous assumptions, showing that this process can be slower and result in a more extended gas distribution than previously thought. In addition, I analytically demonstrated that disc formation can be accelerated if the stellar matter is significantly magnetized. I then highlighted the impact of hydrodynamical instabilities on the debris that can cause an efficient mixing with the surrounding gas, likely dimming the associated flare. Finally, I numerically studied the disruption of magnetized stars, proving that it can produce a thick debris distribution or result in a magnetically amplified remnant. Show less
Improvements of weak gravitational lensing shape measurements are presented and some used for data analysis. Accurate estimates of masses are calculated for clusters of galaxies and member... Show moreImprovements of weak gravitational lensing shape measurements are presented and some used for data analysis. Accurate estimates of masses are calculated for clusters of galaxies and member galaxies. Show less
De Nederlandse fysicus Jaap Kistemaker slaagde er in 1952 voor de eerste keer in om uranium te verrijken. Dat was het begin van een lange reeks experimenten die er uiteindelijk voor zorgden dat... Show moreDe Nederlandse fysicus Jaap Kistemaker slaagde er in 1952 voor de eerste keer in om uranium te verrijken. Dat was het begin van een lange reeks experimenten die er uiteindelijk voor zorgden dat Nederland een sterspeler kon worden op de internationale markt voor verrijkt uranium. De ultracentrifugetechnologie stond aan de wieg van het consortium Urenco, een succesvol samenwerkingsverband tussen Duitsland, Engeland en Nederland. Jaap Kistemaker en uraniumverrijking in Nederland schetst de moeizame weg die Kistemaker af moest leggen. Geconfronteerd met geldnood, bureaucratie en verregaande geheimhouding ten tijde van de ontluikende Koude Oorlog, was het geen eenvoudige zaak om het project in de lucht te houden. Daarnaast toont het boek overtuigend aan dat wetenschap niet alleen afhankelijk is van toeval en doorzettingsvermogen, maar ook dat het natuurwetenschappelijk onderzoek na de oorlog een ingrijpende transformatie onderging. Show less
Galaxies are environments where gas coalesces, cools, and is converted into stars. However, it remains unclear the exact mechanisms through which galaxies acquire, redistribute and lose their... Show moreGalaxies are environments where gas coalesces, cools, and is converted into stars. However, it remains unclear the exact mechanisms through which galaxies acquire, redistribute and lose their gas. The fresh gas that flows into galaxies is primarily composed of Hydrogen and Helium. But because a galaxy’s stars synthesize metals (elements heavier than Hydrogen and Helium), the diffuse gas in galaxies also becomes polluted with these new elements. As a result, by measuring the metal content (metallicity) of gas in galaxies, we can study the history of the gas flows. It is generally thought that the amount of gas in galaxies sets the rate at which stars are formed. Consequently, as the gas is exhausted, star formation rate will slow. Previously thought to be true for galaxies as a whole, our work suggests that this equilibrium may exist on much smaller scales within galaxies today. In this thesis we develop and apply a method that accounts for the blurring caused by the Earth’s atmosphere, which allows us to infer the true metallicity of more distant galaxies. With this we are able to show that, with respect to metallicity, the largest galaxies in the past were not dissimilar to those today. Show less
Polycyclic aromatic hydrocarbons (PAHs) are the most abundant class of organic compounds in space. The PAH field evolves from the constant interaction between experimentalists, theorists,... Show morePolycyclic aromatic hydrocarbons (PAHs) are the most abundant class of organic compounds in space. The PAH field evolves from the constant interaction between experimentalists, theorists, modellers and observers. While laboratory research and quantum chemical calculations together set up the molecular properties of PAH species, astronomers on the other hand, retrieve as much information as possible from the space observations. Nowadays, the PAH field is advanced enough to start implementing all these results into astronomical models, in order to study PAHs from a molecular groundwork. In this regard, the research projects presented in this thesis do precisely that. They constitute a first attempt to gather the vast current knowledge available on specific PAH molecules (not using generic properties), and put it in an astrophysical context, and with it, target some of the key subjects of the field such as: the existence of the so-called grandPAHs in space; the role of PAHs in the formation of molecular hydrogen in photodissociation regions; the abundance of superhydrogenated PAHs and their contribution as a carrier of the 3.4 micron band observed in photodissociation regions; and the deuterium fractionation in PAHs, and their consequent role in explaining the observed deuterium abundance in the local interstellar medium. Show less
The thesis "Spinning Worlds" is about the characterisation of two types of gas-giant exoplanets: Hot Jupiters, with orbital periods of fewer than five days, and young, wide-orbit gas giants,... Show moreThe thesis "Spinning Worlds" is about the characterisation of two types of gas-giant exoplanets: Hot Jupiters, with orbital periods of fewer than five days, and young, wide-orbit gas giants, with orbital periods as long as thousands of years. The thesis is based on near-infrared observations of 1 hot Jupiter and 3 wide-orbit gas giants at high spectral resolution. The observing strategies and the analyses are unique for the two types. For the hot Jupiter, HD 209458 b, the focus is the vertical temperature structure of the atmosphere. This particular hot Jupiter was previously thought to have an atmospheric layer where the temperature increases with altitude, but we found evidence against the existence of such a layer. The three wide-orbit gas giants are all in the early stages of their lives, and we measured their rotation and found a correlation with age: The very youngest objects rotate more slowly than the slightly older (20 million years) objects. We interpret this as the initially hot and bloated exoplanets cooling down and contracting, causing them to spin-up, until the contraction slows down as they approach a radius comparable to that of Jupiter. Show less
Whereas the extreme conditions of the first minutes after the Big Bang have produced nearly all the hydrogen and helium in the Universe, heavier elements - or metals - are synthesised in the... Show moreWhereas the extreme conditions of the first minutes after the Big Bang have produced nearly all the hydrogen and helium in the Universe, heavier elements - or metals - are synthesised in the core of stars and in supernova explosions. Currently, however, the behaviour of supernovae (and their stellar progenitors) is not well understood, and could be better constrained by measuring accurately the relative amount of metals they produce. On the other hand, the very hot and diffuse gas - or intra-cluster medium (ICM), glowing in X-ray and detected in the large gravitational potential well of galaxy clusters and groups, is also rich in metals. This means that the building blocks of life, synthesised by billions of supernovae over cosmic times, are present even at the largest scales of the Universe, as they enrich the ICM. In this thesis, I show how measuring the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni in a sample of nearby, relaxed galaxy clusters, groups, and ellipticals observed with XMM-Newton (the CHEmical Enrichment Rgs Sample) helps to better understand Type Ia and core-collapse supernovae, as well as the history and conditions of the ICM enrichment in general. Show less
This study examines the provenance of the mineralogy and palaeontology collections of Teylers Museum in Haarlem. These objects, combined with the thousands of handwritten labels that have been... Show moreThis study examines the provenance of the mineralogy and palaeontology collections of Teylers Museum in Haarlem. These objects, combined with the thousands of handwritten labels that have been preserved, most of which date from the 18th century, are silent witnesses to a largely forgotten world of collecting practices, classifications, academic networks, commercial practices, debates on the nature of fossils and the formation of the earth’s crust, and much more besides. My research is an attempt to reveal the world behind these objects, all of which were once collected for Teylers Museum by the first Director Martinus van Marum (1750-1837). It seeks to give the collection back its voice. Combining the financial records of the Teylers Foundation with the minutes of meetings held by the directors and Teylers’s Second Society, as well as Van Marum’s travel journals, written records of public lectures, correspondence, and other manuscripts made it possible to reconstruct his purchases and to match labels to objects. When the entirety of Van Marum’s geological endeavours is surveyed, he emerges as more of a follower of scientific developments than a knowledge producer. He published very few articles in this field, and the ideas he presented in them were seldom new and sometimes misconceived. His activities in geology were not on a par with his great achievements in physics and chemistry. However, by virtue of his positions in the Teylers Foundation and the Holland Society of Sciences, as well as his publications on plant physiology and static electricity, he was regarded as one of the most influential scientists of his day. Show less
