This thesis explores the theoretical and observational properties of distant massive galaxies that harbour active black holes in their centres and shine brightly at radio wavelengths. These radio... Show moreThis thesis explores the theoretical and observational properties of distant massive galaxies that harbour active black holes in their centres and shine brightly at radio wavelengths. These radio galaxies are some of the rarest objects in the Universe, and studying them reveals more about the formation and evolution of massive galaxies and black holes in the Universe. In Chapter 2, we model faint radio galaxies at record distances (high redshifts) using a simple model to characterise the overall evolution of radio galaxies. We find that our model replicates well the properties of radio galaxies that are nearer to us. This gives us confidence in the predictions at higher redshifts (larger distances), where data is scarce. In Chapter 3, we compile a list of promising distant radio galaxies using all-sky radio datasets. We present observations for these candidates at a high resolution. In Chapter 4, we report the discovery of the most distant radio galaxy observed till date, TGSS J1530+1049. The galaxy’s distance is confirmed using data from various telescopes. In Chapter 5, we present a detailed study of other distant radio galaxies from our initial sample, showing their properties to be different from brighter radio galaxies. Show less
For centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way -... Show moreFor centuries astronomers studied the Universe by collecting light. Nowadays, we are living in times of great technological advancements, which allow us to explore our Universe in a new way - though gravitational wave radiation. There are many gravitational wave sources in our own Galaxy, the Milky Way. For example, white dwarf stars in tight binary systems spinning around each other in less than 1 hour. LISA is a future ESA mission, that will detect a large variety of gravitational wave sources including Galactic double white dwarfs. Although quite faint, double white dwarfs can also be seen by optical telescopes. Thus, astronomers call them “multi-messenger” sources. This means that we can collect information from them using more than one messenger: electromagnetic waves, messengers of the electromagnetic field, and gravitational waves, messengers of the gravitational field. This thesis proposes to use gravitational wave signals from Galactic double white dwarfs to study the Milky Way and its neighbourhood. In particular, it explores how by collecting many electromagnetic and gravitational wave signals from thousands to millions of binary double white dwarfs spread all across our Galaxy, we can perform multi-messenger Galactic Astronomy and learn about the structure and history of the Milky Way. Show less
Astronomical observations of cold regions in the universe show a rich inventory of ices. Part of these ices may end up on planets like our own, but in that journey they will be exposed to... Show moreAstronomical observations of cold regions in the universe show a rich inventory of ices. Part of these ices may end up on planets like our own, but in that journey they will be exposed to considerable amounts of radiation. As water is the main component of these ices, the optical and photochemical properties of water ice largely determine how the radiation affects the molecules embedded in the ice. In this thesis, water ice is investigated as a host for photochemical reactions. A new laboratory setup is constructed, and two types of molecules are studied: glycine, an amino acid, and triphenylene, a polycyclic aromatic hydrocarbon. The photochemistry upon exposure to ultraviolet radiation is studied using UVvis and infrared spectroscopy. In addition, the optical properties of water ice are constrained in the UV-vis range, resulting in high-resolution optical constants, relevant for all ice-rich environments - from far away in space to our atmosphere. Water itself does not absorb light in this range, but as most organic molecules do, and are destroyed by radiation in this range, this is of high importance for molecules within the ice. Show less
When observing star-forming galaxies, we are not only seeing stellar light, but we also see how this interacts with galactic gas and dust. This thesis contains studies of the stellar, nebular and... Show moreWhen observing star-forming galaxies, we are not only seeing stellar light, but we also see how this interacts with galactic gas and dust. This thesis contains studies of the stellar, nebular and dust properties of low mass star-forming galaxies. We analyse data from the first statistical sample of low mass galaxies with stellar masses down to 10^7 solar masses, and investigate the emission from the stellar populations and their impact on and properties of the ionised surrounding gaseous nebulae, in order to understand the amount of ionising photons that are produced and the fraction of these that can escape from the galaxies. Since the stellar masses in low-mass systems may be stochastically sampled, we predict the influence of this on their nebular emission lies, and in particular on the derivation of their gas metallicity (the abundances of elements heavier than hydrogen and helium in the gas). To interpret observations of galaxies correctly, it is important to know the amount of interstellar dust grains, and its impact on the stellar and nebular light. We therefore finalise this thesis with a new method to derive dust properties in star-forming galaxies. Show less
The Low Frequency Array enables studies of low-frequency carbon radio recombination lines with unprecedented sensitivity, spectral and spatial resolution. In this thesis we benefit from the... Show moreThe Low Frequency Array enables studies of low-frequency carbon radio recombination lines with unprecedented sensitivity, spectral and spatial resolution. In this thesis we benefit from the capabilities of LOFAR to study the cold interstellar medium through carbon radio recombination lines. We find that at low-frequencies these lines trace cold gas, associated with the C+/CI/CO interface of photo-dissociation regions. This opens up the possibility to study these interfaces over large regions of the Milky Way. Show less
The thesis explores how interstellar chemistry evolves as a function of time and changing physical architectures during the formation of stars. The motivation behind the work is an aspiration to... Show moreThe thesis explores how interstellar chemistry evolves as a function of time and changing physical architectures during the formation of stars. The motivation behind the work is an aspiration to better understand how the Solar System came to be, which processes led to its chemical composition and ultimately, what enabled life to evolve on Earth. Show less
This thesis presents pioneering work on the panchromatic emission of some of the most luminous galaxies in the early Universe: star forming galaxies and active galactic nuclei. Using state-of... Show moreThis thesis presents pioneering work on the panchromatic emission of some of the most luminous galaxies in the early Universe: star forming galaxies and active galactic nuclei. Using state-of-the-art statistical methods and new-generation radio-to-X-rays instruments, this thesis expands the parameter space covered by current multi-wavelength studies of galaxy evolution. In particular, this thesis pushes three different frontiers. The statistical frontier is explored by developing a sophisticated statistical tool to robustly recover the parameters required to model multi-wavelength emission. The wavelength frontier is pushed forward by exploring galaxy evolution from the new spectral window at low-frequency radio, opened by the LOFAR instrument. Finally, the resolution frontier will be pushed by exploring the distribution of emission components across the spectrum using a combination of high-resolution ALMA and HST imaging. Show less
This thesis describes the Multi-site All-Sky CAmeRA (MASCARA), which consists of two small robotic telescope designed to detect exoplanets around the brightest stars in the sky. These telescopes... Show moreThis thesis describes the Multi-site All-Sky CAmeRA (MASCARA), which consists of two small robotic telescope designed to detect exoplanets around the brightest stars in the sky. These telescopes search for exoplanets by continuously taking images of the sky and measuring the brightness of stars in these images, searching for the characteristic dimming that occurs when a planet passes in front of the star, blocking some of the starlight. An introduction to exoplanets is provided in chapter 1. The optical and mechanical design of the MASCARA telescopes, as well as the image processing algorithms, are described in chapter 2. The primary and secondary calibration methods used to remove systematic effects from the brightness measurements, as well as the transit search algorithm used, are described in chapter 3. The first planets discovered by MASCARA, two hot Jupiters orbiting the stars HD 201585 and HD 185603, are described in chapters 4 and 5. Show less
This thesis examines the link between simple molecules and the underlying structure and chemistry within protoplanetary disks - the birthplaces of planets. The chapters describe the analysis and... Show moreThis thesis examines the link between simple molecules and the underlying structure and chemistry within protoplanetary disks - the birthplaces of planets. The chapters describe the analysis and interpretation of data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) interferometer, primarily in two disks around the young stars HD 163296 and HD 169142. Observations of dust and molecular gas probe the relationship between the dust structure, the gas distribution, and the chemical processes that give rise to the gaseous species. In the disk around HD 169142, substructure in the millimeter dust and carbon monoxide gas strongly suggests the presence of giant planets sweeping up disk material. Meanwhile, molecular ions reveal previously hidden structure in the gas deep within the disk beyond the millimeter dust edge. In the disk around HD 163296, carbon monoxide and the simple organic molecule formaldehyde show radial variation connected to the millimeter dust edge. The organic molecule methanol is not detected in the disk, suggesting differences in the production of formaldehyde and methanol. This thesis concludes that the distribution of simple molecules is connected to the dust size distribution in disks, while more complex molecules remain elusive but can still provide constraints on disk chemistry. Show less
This thesis describes the development and validation of new high-contrast imaging techniques, with the ultimate goal of enabling the next generation of instruments for ELT-class telescopes to... Show moreThis thesis describes the development and validation of new high-contrast imaging techniques, with the ultimate goal of enabling the next generation of instruments for ELT-class telescopes to directly image Earth-like extra-solar planets orbiting around nearby stars. In particular, we focus on developing new focal-plane wavefront sensing techniques and liquid crystal optics to achieve high-precision adaptive optics control which is capable of stabilising the entire instrument. We demonstrate that one such hybrid optical concept, the coronagraphic Modal Wavefront Sensor (cMWS), is capable of providing real-time, broadband (500-900 nm) control of non-common path aberrations during on-sky observation. We also demonstrate via both realistic simulations and laboratory testing that the focal-plane sensing technique of “Fast and Furious” phase diversity provides a robust, software-only solution to unforeseen, performance-limiting wavefront control issues such as the low-wind effect seen in the SPHERE instrument at the VLT. Lastly, we characterise the extinction profile of the VLT-SPHERE-IRDIS apodised Lyot coronagraph using observations of the minor planet Ceres, and use this to devise a calibration scheme which optimises the accuracy with which polarised signals from the innermost regions of protoplanetary disks may be retrieved. Show less
This thesis is about cosmological inflation and its relation to observations. In part I we study the observational consequences of an additional scalar field besides the inflaton field. In... Show moreThis thesis is about cosmological inflation and its relation to observations. In part I we study the observational consequences of an additional scalar field besides the inflaton field. In particular, we focus on several different regimes where we vary both the coupling between the fields and the mass of the second field. In part II we perform a statistical analysis to understand whether we can extract some of the traces of new physics present during inflation from the three-dimensional map of galaxies in our universe. Show less
A remarkable population of short period transiting rocky exoplanets with equilibrium temperatures on the order of 2,000 K has recently been discovered. Their high temperatures make them very... Show moreA remarkable population of short period transiting rocky exoplanets with equilibrium temperatures on the order of 2,000 K has recently been discovered. Their high temperatures make them very different to the planets in our solar system. In particular, hot super-Earths are thought to have mineral atmospheres that are produced by the vaporisation of their surfaces, or large exospheres that are produced by sputtering of their exposed surfaces by intense stellar winds. Additionally, some smaller, low surface gravity hot rocky exoplanets have been found to be actively disintegrating and forming 'comet-like' dust tails that produce asymmetric transit light curves with forward scattering features. Since the gas and dust originates from the planetary surface, these planets offer the tantalising prospect of enabling us to probe the surface composition of rocky planets. The purpose of this thesis is to work towards this goal by searching for gas around hot rocky exoplanets with observational spectroscopy (Chapters 2 and 5), and by modelling the transit light curves produced by their 'comet-like' dust tails (Chapters 3 and 4). Show less
This thesis aims to enhance our understanding of galaxies by testing theoretical models of galaxy formation against observations, particularly in the cases of extreme systems which have been found... Show moreThis thesis aims to enhance our understanding of galaxies by testing theoretical models of galaxy formation against observations, particularly in the cases of extreme systems which have been found to have an excess of baryonic mass in their central regions, in the form of either supermassive black holes or stellar populations, thus harbouring "monsters" in the deep. To this end we use the EAGLE project, a suite of cosmological, hydrodynamical simulations of galaxy formation and evolution that have been calibrated to reproduce the number density and sizes of galaxies in the Universe. We find that galaxies with supermassive black holes that are much more massive than expected given their stellar mass are predicted to exist and they become overmassive through early formation and/or tidal stripping from more massive galaxies. Recent evidence for excess stellar mass in the centres of high-mass, early-type galaxies has fueled claims that the stellar initial mass function (IMF) may be variable. We test the consequences of such variations in the EAGLE model by performing two additional simulations in which the IMF becomes respectively top-heavy or bottom-heavy in high-pressure environments. The strong effects of such variations are explored in terms of scaling relations between, and within, galaxies. Show less
In this thesis, we present new laboratory data of interstellar dust analogues. These measurements, were transformed to interstellar dust models and were used to fit the spectra of low-mass X... Show moreIn this thesis, we present new laboratory data of interstellar dust analogues. These measurements, were transformed to interstellar dust models and were used to fit the spectra of low-mass X-ray binaries located in the Galactic center neighborhood in order to determine the dust properties along those lines of sight. In these spectra, we focus in particular on the Si K-edge. The XAFS features in the Si K-edge offer a range of possibilities to study silicon-bearing dust, such as investigating the crystallinity, abundance and the chemical composition. We also present a study on the prospects of observing carbon, sulfur, and other lower abundance elements (namely Al, Ca, Ti and Ni) present in the interstellar medium using future X-ray instruments. We simulated data of instruments with characteristics of resolution and sensitivity of the Athena, XARM and Arcus concepts. Lastly, we explore the theory of X-ray scattering for a new parameter space where the small angle approach is no longer valid and where the size distribution of the dust includes large (> 1 micron) particles. We apply this theory to the environment of stellar debris disks where such conditions apply. We use as a best test case the debris disk of AU Microscopii. Show less
This thesis addresses the chemical processes that determine the compositions of giant planet atmospheres. Connecting the observed composition of exoplanets to their formation sites often involves... Show moreThis thesis addresses the chemical processes that determine the compositions of giant planet atmospheres. Connecting the observed composition of exoplanets to their formation sites often involves comparing the observed planetary atmospheric carbon-to-oxygen (C/O) ratio to a disk midplane model with a fixed chemical composition. In this scenario chemistry during the planet formation era is not considered, and the C/O ratios of gas and ice in disk midplane are simply defined by volatile icelines in a midplane of fixed chemical composition. However, kinetic chemical evolution during the lifetime of the gaseous disk can change the relative abundances of volatile species, thus altering the C/O ratios of planetary building blocks. In my chemical evolution models I utilize a large network of gas-phase, grain-surface and gas-grain interaction reactions, thus providing a comprehensive treatment of chemistry. In my talk I will show how chemical evolution can modify disk miplane chemistry and how this affects the C/O ratio of giant planet-forming material. I will argue that midplane chemical evolution needs to be addressed when predicting the chemical makeup of planets and their atmospheres. And as an extra, I will propose that chemical evolution can help constrain the formation histories of comets. Show less
This thesis investigates how galaxies form and what diversifies the evolutionary histories of galaxies. The first part of this thesis describes the identification of luminous galaxies in the early... Show moreThis thesis investigates how galaxies form and what diversifies the evolutionary histories of galaxies. The first part of this thesis describes the identification of luminous galaxies in the early Universe and the follow-up study of their properties with the Very Large Telescope, ALMA and the Hubble Space Telescope. Luminous galaxies are assembling through merging of multiple components and heavy elements as carbon are already in place relatively shortly after galaxies have formed. The second part describes the study of the Lyman-alpha escape fraction of galaxies at the peak of star formation history. The Lyman-alpha escape fraction is generally low, except for rare massive galaxies with AGN activity or for low mass galaxies. This implies that Lyman-alpha radiation escapes more efficiently in the early Universe, when galaxies tend to be less massive with a lower dust content. The final part of this thesis is a theoretical investigation of the co-evolution of dark matter halos and galaxies in the cosmological hydrodynamical EAGLE simulation. Galaxy stellar mass growth is driven by both the mass and formation time of dark matter halos. As a result, present-day growth rates of galaxies are coherent with the long time-scale histories. Show less
Pulsars were first discovered in 1967 and since then the population has grown and expanded over several wavelengths. In this thesis three different X-ray pulsars and three black widow radio pulsars... Show morePulsars were first discovered in 1967 and since then the population has grown and expanded over several wavelengths. In this thesis three different X-ray pulsars and three black widow radio pulsars and their evolution has been examined. The pulsars in this work all show variability that was not expected of their type of sources, e.g. the pulsar 2A 1822-371 is found to have an orbital period that is expanding over time more than what is expected. We suggest this to be due to the pulsar being a super Eddington source. Another part of the thesis uncovers that the magnetic field may have a significant influence in the behavior of the pulsars. Low magnetic field pulsars often show a correlation between their pulse phase and their flux, whereas we find that this correlation is not present in high magnetic field pulsars. This could mean that the hot spot, where the pulsations origin, is not moving in high magnetic field pulsars but could be moving in low magnetic field pulsars. The first black widow pulsars discovered had unstable timing solutions, whereas the black widow pulsars in this work all have stable timing solutions, and we look into possible explanations to this difference. Show less
Laboratory, observation and modeling work on the dissociation of polycyclic aromatic hydrocarbons in interstellar environments and the formation of new molecular species through the fragmentation... Show moreLaboratory, observation and modeling work on the dissociation of polycyclic aromatic hydrocarbons in interstellar environments and the formation of new molecular species through the fragmentation process. Show less
This thesis is about the study of hydrocarbons via infrared spectroscopy. Hydrocarbons play an important role in the chemistry of a variety of astronomical environments from the diffuse... Show moreThis thesis is about the study of hydrocarbons via infrared spectroscopy. Hydrocarbons play an important role in the chemistry of a variety of astronomical environments from the diffuse interstellar medium to dense hydrocarbon atmospheres of solar system bodies (e.g., planetary atmospheres of Jupiter and Saturn’s moon Titan) and exoplanets. For most astronomical objects, the determination of chemical abundances, and consequently an understanding of the chemical evolution relies upon the observation of molecular spectra. However, to date astronomical models need to make assumptions, because not all of the molecules expected have been observed. This is due, in part, to a lack of accurate spectral data, which is needed for unambiguous identification. Using a combination of high-resolution infrared experiments and/or high level ab initio calculations of vibration frequencies and ground state spectroscopic constants, the infrared spectral data of HC2H, HC4H, HC6H, HC8H, C3H4, c-C3H3+ and Dn-PAHs (polycyclic aromatic hydrocarbons, PAH) are studied and presented, in order to fill in some of the missing spectral data. Show less
Large areas of space are filled by molecular clouds that consist of gas and dust grains that are the remnants of dead stars. When these clouds start collapsing, the decreasing temperature and... Show moreLarge areas of space are filled by molecular clouds that consist of gas and dust grains that are the remnants of dead stars. When these clouds start collapsing, the decreasing temperature and increasing density cause gas particles to start accreting onto dust grain surfaces. This results in layered geometries of partially mixed ices on top of the grains that act as molecule reservoirs and cryogenic catalysts on which both simple and complex molecules form in surface reactions. These grains form the material from which celestial bodies form. A good understanding of the elementary processes taking place in dark interstellar clouds, therefore, is necessary to understand the chemical inventory of stellar systems, like our own Solar system.This thesis focuses on laboratory studies investigating the surface chemistry of CO-rich ices on dust grains at temperatures as low as 10 K. The formation mechanisms of complex organic molecules (COMs) are investigated by non-energetic processes (e.g., hydrogenation) and energetic processes (e.g., photolysis). Moreover, the net transfer of the newly formed hydrogenated species from grain surfaces into the gas phase through non-thermal desorption is investigated to link the detection of COMs in the gas phase to their formation in the solid state. Show less
