Examples of PhD projects available

An overview

There will be several PhD positions open for application with a deadline of November 15, 2023. For details of the application procedure see this page. The positions are available in all the research areas in which the Observatory is active. This page will give a broad overview of possible research projects . However, research in different areas is possible and not all projects that might be offered are listed. The faculty research interests provides more background information.

  • Small-scale galaxy-galaxy lensing
    Supervisor: Henk Hoekstra
    Description: How galaxies populate dark matter halos is an area of active study, because it helps to understand galaxy formation and to improve cosmological parameter estimates from large surveys, such as the one carried out by the recently launched Euclid mission. A key quantity for such comparisons is the stellar mass of galaxies, which is typically inferred indirectly through the modelling of stellar populations. A more direct measurement via gravitational lensing would allow us to test the assumptions made, and would lead to more reliable results. In this project, we will exploit Euclid's unique ability to determine the lensing signal on very small scales to extract stellar masses of ensembles of galaxies for the first time. This technique could also help us study the tidal stripping of dark matter halos in dense environments. The work involves advancing small-scale lensing analysis tools (like measuring the shapes of galaxies in dense environments) and applying these to the Euclid data.

  • Constraining models of intrinsic alignments
    Supervisor: Henk Hoekstra
    Description: Gravitational lensing is not the only process that introduces correlations in the shapes of galaxies. Tidal interactions acting on galaxies also align them, compromising a straightforward interpretation of the observed cosmological weak lensing signal, such as the one we aim to measure with the recently launched Euclid mission. This intrinsic alignment signal can usually be measured directly by selecting small samples of galaxies that are close in redshift. While spectroscopic measurements are well-suited for this purpose, further information can be garnered from the Euclid data using photometric samples with more galaxies and well-characterised redshift distributions. The aim of this project is to measure the alignment signal as a function galaxy properties and redshift and use the results to inform models for the alignment signal and to confront predictions from cosmological simulations.

  • Statistical Inference Techniques for Euclid-related science
    Supervisors: Elena Sellentin, Koen Kuijken
    Description: A PhD position will be available for research on cosmology with the Euclid mission to look into statical inference techniques, including building emulators for the Euclid likelihood, non-Gaussian statistics, and field-level analyses. Euclid has only recently been launched and has been designed to study dark matter, dark energy, and galaxy evolution. and will map out the large-scale structure and matter distribution to unprecedented precision, using deep galaxy imaging and gravitational lensing. It will require major advances in measurement techniques, statistical inference methods and cosmological simulations.

  • Retrieving the Secrets of Exoplanet Interiors
    Supervisor: Yamila Miguel
    Description: We are in an unprecedented era for studying giant exoplanets. Over 5,000 exoplanets have been discovered, and numerous chemical species identified in their atmospheres. Current space facilities, such as TESS, Cheops, and JWST, are advancing our understanding, and future projects like Plato, Ariel, and ground-based facilities like ELT are on the horizon. At the same time, our comprehension of the giants within our solar system has evolved significantly. Missions like Cassini and Juno have been transformative, providing radical insights into Jupiter and Saturn's interiors. While the astonishing variety of newly discovered exoplanets reshapes our perspective on our solar system, a profound understanding of our native planets is crucial to grasping the fundamental physics of giant planet dynamics.

    In this project, the chosen candidate will develop a retrieval code to delve into the interiors of exoplanets. By combining insights from Solar System studies with the remarkable data obtained from JWST's measurements of exoplanet atmospheres, this project aims to pioneer investigations into the internal structures of planets. Objectives include determining core masses and obtaining precise metallicities, both critical to our understanding of the formation and evolution of giant planets.

    This project relies heavily on modelling and theoretical aspects. As such, candidates with strong programming skills are particularly encouraged to apply.

  • Integrated coronagraphs and wavefront sensors for high-contrast imaging instruments
    Supervisor: Sebastiaan Haffert
    Description: Current direct imaging observations of exoplanets are limited to massive young planets, but the next generation of extremely large telescopes will unlock access to older, more temperate planets with masses and radii more like those in our Solar System. And for the first time, these telescopes will allow us to search for life on exoplanets. However, direct detection of temperate exoplanets is challenging due to the extreme contrast ratio between the planet and star that must be overcome. Therefore, it is crucial to push the technology that enables such observations. In this project the applicant will work together with Dr. Sebastiaan Haffert to develop integrated coronagraphs and wavefront sensors for extreme adaptive optics instruments for the Extremely Large Telescope. The new technology will be tested on-sky at world-leading observatories to demonstrate their potential for the ELT.

  • The space weather around exoplanets
    Supervisor: Aline Vidotto
    Description: Stellar magnetic activity, in the form of high-energy radiation and stellar outflows, drives the space weather around exoplanets. High-energy radiation heats planetary atmospheres, which inflate and more likely escape. Stellar outflows cause pressure confinement around otherwise freely escaping atmospheres. How different is the space weather of exoplanets compared to Earth's? Can we detect signatures of exo-space weather? How does a harsher space weather affect close-in exoplanets and their atmospheres/magnetospheres?

    To tackle questions like these, we are looking for a motivated PhD student to work on the theme of "space weather" using 3D magneto-hydrodynamics simulations. The PhD candidate will develop novel 3D simulations to interpret and guide observations linked to exo-space weather. Our group has expertise in investigating both the host star (simulating stellar winds and coronal mass ejections) and the exoplanet (simulating atmospheric escape), and different projects during the PhD will look at one or both aspects. To learn more about the research of our group, please see our webpage.

  • Uncovering early dusty galaxy formation
    Supervisor: Jacqueline Hodge
    Description: How the nascent stars in young galaxies formed out of the surrounding cold gas is one of the most fundamental questions in astronomy. Yet it has been known since the launch of the first infrared sky surveys that a substantial fraction of the Universe’s high-redshift star formation is heavily enshrouded by dust, making it particularly challenging, historically, to obtain a clear view of star formation in the young (z≥2) Universe. At the same time, our understanding of the molecular gas fueling that star formation is still very limited. In this project, the successful candidate will leverage data from the Atacama Large Millimeter Array (ALMA) to directly trace the fuel for star formation in early galaxies. Combined with brand new observations from the James Webb Space Telescope (JWST)--revealing the hidden stellar populations in these galaxies for the first time--this project aims to provide the first complete, high-definition picture of the past (stars), present (star formation), and future star formation (gas) of young dusty galaxies needed to understand their evolution in the context of hierarchical structure formation.

  • The formation of the earliest massive galaxies
    Supervisor: Jacqueline Hodge
    Description: While our understanding of the dusty star formation and gas content of galaxies is still limited out to z~5, it is almost completely unconstrained at even higher redshifts. There, deep optical and mm-wave surveys have revealed the existence of extremely massive galaxies already within the first Gyr after the Big Bang, with recent James Webb Space Telescope (JWST) results suggesting even more extreme examples and challenging our cosmological paradigm. In this project, the successful candidate will push studies of dust and gas in galaxies to the earliest cosmic epochs, including detecting their molecular gas via CO(3-2) emission and leveraging new JWST data, shedding light on how these galaxies built up their stellar masses so quickly.

  • Discovering Hypervelocity stars with Gaia and Weave
    Supervisor: Elena Maria Rossi
    Description: Hypervelocity stars (HVSs) are observed in the halo traveling at a velocity in excess of the escape speed of our Galaxy. Their trajectory can be traced back to our Galactic Centre and the most likely explanation is that they suffered a dynamical interaction involving our Supermassive black holes (SgA*) and as a result they were ejected from SgA*'s surroundings into the halo. These are very rare stars but very precious to understand the content and dynamics of our Galactic Centre, which is hard to observe directly. The goal of this project is to devise and carry forward the best data mining strategy to find HVS candidates in Gaia catalogues, which is the largest stellar catalogue ever produced. These will be followed up with WEAVE, a multi-object spectrograph installed on the WH 4-meter telescope in La Palma. WEAVE is the ideal instrument for this project and it will start operating this year. Discoveries (or not) of these rare stars will be translated into unique astrophysical knowledge of our Galactic Centre through data modelling. This is mainly an observational project. There is an opening for one position in Elena Maria Rossi’s group in either this project or the following project.

  • Numerical Simulations of Tidal Disruption Events
    Supervisor: Elena Maria Rossi
    Description: Tidal Disruption Events (TDEs) occur when a star is torn apart by the tidal field of a supermassive black hole and results in an extremely bright flare that can be seen at cosmological distances. This is a very data-rich era for TEDs but accurate and consistent models for their emission are missing. This prevents us from using their light to study supermassive black holes and their environments. This project addresses this shortcoming but numerically computing TDE emission for a large range of parameters exploiting the new code RICH. The aim is to understand the physical origin of the optical and UV light (currently unknown) and build a library of models that can be applied to data to extract measurements of supermassive black hole masses. These are of paramount importance for understanding the origin and evolution of supermassive black holes. This Project is theoretical and computational. There is an opening for one position in Elena Maria Rossi’s group in either this project or the previous project.

  • Finding stellar tidal disruption events in Rubin/LSST data: black hole genesis and high-energy neutrinos
    Supervisor: Sjoert van Velzen
    Description: Stellar tidal disruption events provide a unique probe of dormant black holes. With the Vera Rubin C. Telescope, which is scheduled for operations in 2025, we could find thousands of these rare events. We are therefore on the brink of a revolution for this field. However, making this possible will be a tremendous challenge. We will have to push our photometric selection methods to new limits. In this PhD project we will take on this quest. You will work within the TDE group of the Rubin collaboration. The scientific goals of this project are twofold: we will test correlations with high-energy neutrinos and we will use our sample for inference on the black hole mass function, which in turn can be used to constrain the origin of black holes in the early universe.

  • Expert baryonic feedback modelling in Euclid-like surveys
    Supervisors: Marcel van Daalen, Elena Sellentin
    Description: The recently launched Euclid satellite will measure the cosmological weak lensing signal to unprecedented precision - but needs theory to match. Currently, the largest nuisance for connecting the observations to the cosmology of our Universe through theory is the uncertain strength and scale dependence of baryonic feedback processes, such as AGN feedback, which redistribute matter in and around massive haloes. This has so far necessitated either adding many nuisance parameters to marginalise over (leading to a great loss of precision) or cutting small scales out of the analysis (leading to a greatly reduced constraining power). In this project, we choose to instead use a Bayesian approach to model the effect of baryons and feedback on clustering statistics. The Bayesian approach will utilize insights from simulations and external data to derive an accurate and sophisticated likelihood function for Euclid's parameter inference. The applicant should enjoy analysis of simulations, and have an interest in the science case of Euclid.

  • Mapping planetary building blocks in 2D with JWST
    Supervisor: Melissa McClure
    Description: Planets form in disks of gas and dust around nascent stars. The initial building blocks of planets are the icy dust grains that start cold in the outer regions of such "protoplanetary" disks and are radially transported towards the central star. To understand the bulk interior compositions of exoplanets, it is essential to make 2D maps of the distribution and composition of volatile solids in disks as a function of time. These solids are also the likely feedstock of the volatile-enriched planetary atmospheres seen in the Solar System and exoplanetary systems. The goal of this project is to use new JWST data from the Ice Age and MIDAS Cycle 1 programs to make a map of the ice and gas phase abundances in these disks. Modeling for the Ice Age program (Sturm+23c, d, in press) has revealed that radiative transfer models are required to back out ice abundances from JWST ice spectra, due to the complex scattering causing local saturation of the ice features. We also see evidence for mixed ices (CO trapped in CO2/H2O), which changes the location of critical snowlines, and gas emission from the inner disk in the same spectra. Forward radiative transfer models of the combined gas emission and ice absorption would allow us to construct this map and also test theories of radial drift of icy, centimeter sized dust grains by comparing the inner and outer disk abundances of the same molecules.

  • Evolution of galaxies and feedback from supermassive black holes using LOFAR and EUCLID surveys.
    Supervisors: Huub Rottgering, Lingyu Wang (SRON)
    Description: Euclid will be of paramount importance for providing unprecedented huge samples AGNs across a large fraction of cosmic history, determining galaxy size and morphology, mass, star-formation rate, host dark matter halo mass and large-scale environment. LOFAR will detect and map every radio-loud AGN in the Euclid northern sky. With these massive and complementary data sets key questions that we would like to address include: (i) How is the impact of feedback by radio-loud AGN related to the characteristics of the AGN, their host galaxies and environments? (ii) How does the effect of AGN feedback change during the build-up of galaxies and how does it affect the growth of black holes throughout the history of the Universe?

  • Supermassive black holes in the epoch of reionisation
    Supervisors: Huub Rottgering, Joseph Hennawi
    Description: The project is to compile a unique sample of extremely distant (6<z<8) radio-loud AGN located in the Epoch of Reionisation (EoR), study their properties and use them as a tool to study the EoR. The samples will be obtained using a combination of the LOFAR radio surveys, Euclid optical/IR surveys, the wide-field (4m) WHT/WEAVE spectroscopic survey and targeted Keck (10m) spectroscopy – all data/facilities that currently are available. As radio-loud AGN are powered by extremely massive black holes, we will use the data to study one of the bigger questions in astronomy: how is it possible that such massive objects formed so early after the Big Bang? Furthermore, LOFAR absorption spectroscopy of these objects of the redshifted 21 cm HI line will uniquely constrain the distribution of hydrogen in the early Universe, a powerful way to constrain characteristics of the EoR.