This week's PhD colloquia are highlighted.
| Date | Time | Title/Abstract | Speaker | Affil. |
|---|---|---|---|---|
| 15/01 Wednesday BW.0.32 | 14:15 | Big simulations for big problems In this colloquium I investigate cosmology and the large scale structure of the Universe using cosmological simulations. The fields of cosmology, numerical cosmology, structure formation and galaxy clusters are introduced. Then I discus a machine learning method to set up subgrid models in numerical simulations, which I use to set up the FLAMINGO simulation suite. With this method I can calibrate our models directly to the observational data, without the needed of running thousands of hydrodynamical simulations. I then investigate selection effects on galaxy clusters and their impact on cosmology. Finding that for upcoming surveys the careful modeling of your selection effects is very important, and current models do not have the degree of accuracy required to make clear statements about the inferred cosmology. In the final part I will investigate the large scale flows of the universe, and their origin. I find that the mass contained in filaments is the main driver of cosmic dynamics. However for the smaller scale structures, voids also provide an important contribution. | Roi Kugel | Leiden Observatory |
| 05/02 Wednesday BW.0.32 | 14:15 | Gas physics in simulated galaxy clusters Galaxy clusters are the behemoths sitting at the nodes of the cosmic web. They are powerful tracers of the evolution of the Universe, and are often assumed to be simple, well-behaved systems. In this talk I will focus on the gas physics within the clusters, which I probe using both idealized simulations, and the new FLAMINGO simulations. I will show how the choice of hydrodynamic solver influences the survival of cold clouds entrained within a hot wind, a scenario commonly encountered on scales ranging from the ISM to the IGM. Following those idealized simulations, I will introduce FLAMINGO and results to prove that the galaxy groups and clusters reproduce observations. Obtaining accurate masses for these massive haloes is extremely challenging observationally, and in the remainder of the talk I will show where biases in the mass estimate originate, and what we can learn from correlated scatter between different observables from the same object. | Joey Braspenning | Leiden Observatory |
| 03/03 Monday BW.0.32 | 15:15 | The Evolutionary Tale of Gaseous Exoplanets The evolution and fate of gaseous exoplanets are continuously shaped by stellar activity across both short and long timescales. Short-term events, such as stellar flares, produce intense bursts of high-energy radiation that break apart molecules in the upper atmosphere of the exoplanet, driving significant chemical changes. Over longer periods, prolonged exposure to strong stellar irradiation gradually heats the planet, leading to atmospheric escape and potential transformation in its structure and composition. To better understand these processes, we employ (photo)chemical disequilibrium modelling, radiative transfer simulations, and planetary evolution codes to analyse the interiors and atmospheres of gaseous exoplanets. By doing so, we aim to determine how these external influences shape their composition, structure, and observable characteristics, shedding light on their long-term atmospheric evolution. Depending on the type of planet, star, and chemistry considered, these impacts can alter exoplanetary atmospheres significantly over both short- and long timescales. | Amy Louca | Leiden Observatory |
| 22/04 BW.0.31 | The Trials and Tribulations of PAHs in Asteroids Carbonaceous asteroids preserve a record of early solar system processes, where minerals and organic molecules, like polycyclic aromatic hydrocarbons (PAHs), offer clues to planetary evolution and prebiotic chemistry. This thesis explores whether aqueous alteration, liquid water interacting with rock, affects the behaviour of PAHs in asteroids. We examined how PAHs respond to water, mineral surfaces, and internal heat within asteroids through experiments and modelling. Results show that PAHs are chemically stable under asteroidal conditions but can be physically mobilized by water flow, especially where the solubility of PAHs increases with temperature. Smaller PAHs may form carbon-rich globules, as seen in meteorites, while larger PAHs like coronene remain unchanged. PAHs are not promising precursors for amino acids under the investigated conditions. However, other asteroidal conditions may favour reactions and remain unexplored. Ultimately, hydrothermal convection can redistribute stable PAHs and possibly other organics, making temperature a key factor in shaping their fate and distribution in asteroidal parent bodies. These findings clarify the role of water in shaping the distribution, stability, and chemical potential of PAHs in asteroids. | Claudia Giese | Leiden Observatory | |
| 29/04 BW0.32 | Molecular Diagnostics of Dense Regions in Nearby Galaxies This thesis explores the use of molecular line emission as a diagnostic tool for understanding the physical and chemical conditions of the interstellar medium (ISM) in nearby galaxies. Through a combination of high-resolution observations and theoretical modelling, it investigates how molecular tracers—such as HCN, HCO$^+$, CS, and their isotopologues—can be used to differentiate between environments influenced by active galactic nuclei (AGN), starburst (SB) activity, or both. Central to this work is the analysis of molecular line ratios, which vary sensitively with local density, temperature, radiation fields, and chemical processes. By comparing multi-transition observations from instruments including ALMA, PdBI, and JCMT with non-LTE radiative transfer modelling using RADEX and Bayesian inference techniques, this thesis demonstrates how line ratios can be interpreted in terms of physical parameters such as column density, excitation temperature, and gas density. Particular attention is given to the reliability of the HCN/HCO$^+$ ratio as a diagnostic for AGN activity and how spatial resolution influences its interpretation. Additionally, this thesis presents novel insights into the chemical enrichment of galaxies by studying isotopic ratios, especially $^{12}$C/$^{13}$C and D/H, derived from molecular isotopologues. One key result is the first robust detection of a deuterated molecule, DCN, in a non-Magellanic extragalactic starburst environment—NGC 253—revealing deuterium fractionation levels comparable to those in the Milky Way's central molecular zone. This highlights the importance of metallicity and temperature in shaping molecular abundances. Together, the studies presented here refine our understanding of molecular diagnostics in extragalactic environments and underscore the importance of combining observational data with radiative transfer modelling. The findings contribute to a broader effort to decode the molecular signatures of galaxy evolution, feedback, and chemical processing across a range of galactic environments. | Joshua Butterworth | ||
| 02/05 Friday BW0.32 | 10:00 | Cosmic Depth and Detail: Advancing LOFAR imaging workflows to unveil the deep high-resolution universe The Low-Frequency Array (LOFAR) is one of the leading instruments for studying the Universe at the lowest radio frequencies. In this talk, I will first show how its high sensitivity and enhanced calibration strategies can be used to study large-scale structures, by focusing on the origin of a recently discovered radio bridge connecting two pre-merging galaxy clusters. I then shift to smaller angular scales to examine the cosmic evolution of extended radio-loud AGN morphologies, with the goal of gaining deeper insight into their origin and evolution. Part of the results highlight limitations in angular resolution when relying solely on the Dutch LOFAR stations, particularly for detecting and classifying more distant and fainter sources. Motivated by these resolution constraints, the second part of the talk will focus on producing the deepest high-resolution wide-field images with the full European LOFAR, followed by recent advances in data processing strategies and computational techniques that enable even deeper imaging. These results also pave the way for deep sub-arcsecond resolution surveys with LOFAR, opening the entire northern radio sky at unprecedented cosmic depth and detail. | Jurjen de Jong | |
| 30/06 Monday BW.0.39 | 15:00 | TBA TBA | Julia Santos |
For questions and/or suggestions concerning the colloquium series. Please contact Andrew Sellek (e-mail ).