Vorträge, Seminare, Ereignisse

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Over the last years significant advances have been made in our understanding of how and where stars and planets form and how they evolve during their earliest stages, both from a physical and chemical point of view. Deep observations of the gas and ice in the environments in which young stars form demonstrate that these regions are characterised by rich and varied chemistry with high abundances of complex organic molecules – some perhaps even of prebiotic relevance. At the same time, a picture has emerged where the first seeds for planets are planted in protoplanetary disks already during the first few 100,000 years after stars form. But, what is the link between this complex chemistry and the structure of the newly formed protoplanetary disks – and does it have any implications for the origin and composition of planets outside of our own Solar System? In the colloquium I will discuss how our understanding of the earliest stages of star and planet formation has evolved over recent years. In particular, I will focus on how ALMA has helped shedding new light on how the properties of emerging protoplanetary disks may reflect the evolution of protostars and conditions in their natal environments.

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One of the most outstanding problem in today's understanding of the Universe is the nature of the elusive dark-matter (DM) that dominates the matter content. Rotation curves have been used to put forward the concept of DM in the 70s, and have since revealed a potential problem, for the standard CDM model, on small scales (<1kpc) where DM profiles are too flat (cored) compared to predictions. Alternative DM models have been proposed to produce cores naturally. Hence, rotation curves are dark-matter laboratory given that  the shape of RC on intermediate scales (1-5kpc) is a measure of the shape of the inner DM profiles. Measuring the shape of DM profiles in distant marginally resolved galaxies (with z>0) was deemed impossible, but recently, thanks to recent innovations, it has become possible to study the shape of RCs of hundreds of distant galaxies. I will present the most recent innovations, including our recent results from the MUSE 3D spectrograph.

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Making an informed choice between competing physical models becomes increasingly important in the era of precision cosmology. Central to model selection is a trade-off between performing a good fit and low model complexity: A model of higher complexity should only be favoured over a simpler model if it provides significantly better fits. In Bayesian terms, this can be achieved by considering the evidence ratio, enabling choices between two competing models. We generalise this concept by constructing Markovian random walks in model space governed by the logarithmic evidence ratio. This is in analogy to the logarithmic likelihood ratio in parameter estimation problems. We apply our methodology to selecting a polynomial for the dark energy equation of state function based on data for the supernova distance-redshift relation.

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We aim to trace the evolution of eight edge-on star-forming disc galaxies through the analysis of stellar population properties of their (thin and thick) discs. We use Multi-Unit Spectroscopic Explorer (MUSE) observations and full-spectrum fitting to produce spatially resolved maps of ages, metallicities and [Mg/Fe] abundances and extract the star formation histories of stellar discs. Our maps show thick discs that are on average older, more metal-poor and more ?-enhanced than thin discs. However, age differences between thin and thick discs are small (around 2 Gyr) and the thick discs are younger than previously observed in more massive and more quiescent galaxies. Both thin and thick discs show mostly sub-solar metallicities, and the vertical metallicity gradient is milder than previously observed in similar studies. [Mg/Fe] differences between thick and thin discs are not sharp. The star formation histories of thick discs are extended down to recent times, although most of the mass in young stars was formed in the thin discs. Our findings show thick discs that are different from old thick discs previously observed in more massive galaxies or more quiescent galaxies. We propose that thick discs in these galaxies did not form quickly at high redshift, but slowly in an extended time. The thin discs were formed also slowly, but with a larger mass fraction at very recent times.

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