This week's PhD colloquia are highlighted.
|07/09||Interstellar Catalysts and the PAH Universe|
rganic 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.
|Dario Campisi||Leiden Observatory|
|14/09||11:00||High-contrast imaging polarimetry of exoplanets and circumstellar disks|
Abstract to follow.
|Rob van Holstein||Leiden Observatory|
|21/09||11:00||Galaxy Alignments from Multiple Angles|
Weak Gravitational Lensing is a powerful probe to investigate the dark sector of our Universe. It uses the distortion of galaxy shapes of background galaxies 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. An important complication arises because galaxy shapes are not randomly oriented in the sky before being lensed. Instead, galaxies form and live inside dark matter haloes: they are exposed to the tidal fields generated by the surrounding matter distribution, which leads to a coherent alignment on physically close galaxies, called intrinsic alignment. In this colloquium, I will present our investigation of the dependence of intrinsic alignment on galaxy properties using different techniques, and how this should be accounted for when modelling intrinsic alignment in weak lensing studies.
|Maria Cristina Fortuna||Leiden Observatory|
|19/10||11:00||Distant Star Formation in the Faint Radio Sky|
Radio emission constitutes a powerful and dust-unbiased probe of star formation in distant galaxies, and may therefore be used to directly map the cosmic star formation history. At low frequencies, the radio spectrum of galaxies is dominated by synchrotron emission, which shows a tight correlation with galaxy infrared luminosities, calibrating the former as a tracer of star formation. However, to date the exact physical mechanisms here at play remain poorly understood. At high frequencies, a different and more elusive component known as radio free-free emission emerges, which is often heralded as one of the most powerful tracers of star formation available. Meanwhile, the distant radio sky holds more than just star formation, as active galactic nuclei (AGN) may also emit at radio frequencies.
|Hiddo Algera||Leiden Observatory|
|02/11||Exploring the edge|
Matter in the Universe is distributed in the form of a cosmic web and the boundaries of its nodes have been recently recognized as a tractable feature shaped by non-linear gravitational dynamics. In this colloquium, I will first briefly introduce the physics behind this feature, a.k.a. splashback, and present how we can measure it in observations. Afterward, I will discuss measurements and theoretical advancements that I have worked on, shedding light on its connection to the large-scale structure of the Universe, the nature of dark energy, and galaxy formation. I will conclude by describing present challenges and future prospects for this timely research topic.
|Omar Contigiani||Leiden Observatory|
|16/11||15:00||Ice and Gas in Protostellar Clouds and Planet-forming Disks - A Combined Laboratory and Observational Study|
How did life originate on Earth? Are we alone? These fundamental questions trigger our curiosity and in my colloquium I will present my research that aims to take steps toward a better understanding of (organic) molecules in star- and planet-forming regions. Here are a few teasers of the subjects that I will touch upon: the preparation in the lab for the detection of complex organic molecules with the James Webb Space Telescope, the origin of gas-phase formaldehyde in protoplanetary disk through the eyes of ALMA, and the interaction between gas-phase CO and solid-state OH radicals on the surface of water ice.
|Jeroen Terwisscha van Scheltinga||Leiden Observatory|
|30/11||11:00||UV Photodesorption and Photoconversion of Interstellar Ices - the laboratory perspective|
Among thousands of detected exoplanets are ones which are Earth-like, with a similar rocky composition and a temperature allowing to sustain liquid water. This invites to revisit the question asked since the dawn of times: is it possible that life originated on other planets as well? To address this question, it is important to understand the chemical evolution of matter during the process of star and planet formation. In this talk I will present a series of experimental studies which allow to quantitatively determine the role of VUV radiation on interstellar ice analogues, in the context of the early stages of the stellar formation cycle. Topics that are discussed focus on the formation of new complex molecules, accurate photodesorption rates as well as an explanation for the large amounts of molecular oxygen ice found on comets in our solar system.
|Michal Bulak||Leiden Observatory|
For questions and/or suggestions concerning the colloquium series, please contact Ian Roberts (e-mail )