Vorträge, Seminare, Ereignisse

Abstract
Pulsar Winds and the nebulae which they energize (PWN) are among the most enigmatic objects in astrophysics. They consist of a relativistic, magnetized, electron-positron plasma that forms a compact cloud surrounding young pulsars. Their nonthermal synchrotron and inverse-Compton emission is detected from the radio band to very high energy (TeV) gamma-rays, where they are the dominant galactic source population. The radio-to-infrared spectra of PWN are flat, indicating a remarkably efficient particle acceleration mechanism, able to transfer most of the system energy into a tiny fraction of particles. Despite decades of research, the mechanism responsible for accelerating these particles has remained elusive, and poses one of the greatest challenges in particle acceleration theory. In this talk I will give an introduction to the physics of pulsar winds, and describe recent work on the acceleration mechanisms thought to be at work. These include not only variants of the well-known first-order Fermi mechanism, but also "inductive acceleration", which may explain the mysterious gamma-ray flares from the Crab Nebula, discovered in 2011 by the Agile and Fermi satellites.

Abstract
Tracing matter and chemical elements in the Universe is critical for understanding the formation of the first galaxies, the formation and growth of supermassive black holes, and ultimately the evolution of galaxies like our Milky Way. Throughout the history of the universe, large-scale gas flows have moulded the arms of spiral galaxies, formed the bulges of the most massive galaxies in the universe, fed supermassive black holes in the centers of galaxies, fueled generation upon generation of new stars, and enriched the intergalactic medium with metals. The physics and impact of these processes can now be traced through new efficient, wide-field 3D integral field spectrographs. We use multi-object integral field spectroscopy to build the largest local sample of galaxies with wide 3-dimensional imaging spectroscopy. We combine our local results with insights into the early universe probed through gravitational lensing and adaptive optics. I will present the latest results from our large local and high-z 3D surveys to understand the relationship between gas inflows, galactic-scale outflows, star-formation, chemical enrichment, and active galactic nuclei in galaxies. I will finish by discussing how this field will be transformed in the JWST and ELT era.

Abstract
With ALMA and high-contrast optical/IR imaging, protoplanetary disks are revealed to be structured objects. They display rings, spirals, vortices and warps. These structures appear to be extremely well-defined and often have high contrast. This poses the question: what processes cause these conspicuous structures? Are these signs of planet formation? Or do they betray the existence of just-born planets in these disks? In this talk I will discuss these observations and some theoretical models that attempt to explain them. I will show that these structures indicate that dust “pebbles” are being moved around and are trapped in so-called “pressure traps”. I will show that planetary/substellar companions perturb the disk, but that also disk-internal processes can explain some of the ringlike dust traps. Finally I will discuss some ideas to explain the strong warps seen in some of these protoplanetary disks.

Abstract
Understanding the physical mechanisms driving the formation and evolution of galaxies in a cosmological context represents one of the most important yet unresolved questions of modern astrophysics. Different methods have been developed over the years to link the physical properties of galaxies to the dark matter haloes in which they reside. I will give a brief overview of the aims and limits of these methods, with particular emphasis on semi-analytic models of galaxy formation. I will then review recent developments of our model for GAlaxy Evolution and Assembly (GAEA), and discuss the role of various physical processes in shaping the measured evolution of the galaxy stellar mass function and mass metallicity relation. I will overview our recent work to include a treatment for the partition of cold gas in its atomic and molecular gas components, and a variable stellar Initial Mass Function. I will conclude by discussing open problems and future perspectives.