Vorträge, Seminare, Ereignisse

Abstract
Lorentz symmetry is a fundamental pillar of General Relativity and Particle Physics. Nonetheless, certain theories of quantum gravity involve some degree of Lorenz violation which may have significant consequences on all scale. It is hence worthwhile to explore the observable signatures of Lorentz violations on the dynamics of the low energy spectrum of the theory. I will consider the case of a Lorentz violating vector field acting on the dark matter component of a satellite galaxy orbiting in a host halo and discuss the key observational signatures such as modifications to the line of sight velocity dispersion, mass profiles and shapes of satellites.

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I will describe the numerical efforts to simulate galaxies with the code AREPO across an unprecedented range of halo masses, environments, evolutionary stages and cosmic times. In particular, I will focus on the IllustrisTNG project, a collaboration among Heidelberg, Munich, New York and Boston. There we are aiming to simulate a series of three gravity+magnetohydrodynamics cosmological volumes (50, 100, 300 Mpc a side, respectively) capable of both resolving the inner structures of galaxies as small as the classical dwarfs of the Milky Way, as well as of sampling the large scale structure of the Universe with thousands among groups and clusters of galaxies. I will briefly review what is explicitly and empirically solved in gravity+magnetohydrodynamics simulations for galaxy formation in a cosmological context and what is required and what it means to “successfully” reproduce populations of galaxies which resemble the real ones. I will therefore show preliminary results from the IllustrisTNG simulations, by focusing on the assembly of the most massive structures in the Universe, the build up and characterisation of the faint stellar envelopes around galaxies, the connections of the latter to their host DM haloes, and our theoretical expectations for the distribution of dark matter (DM) and stars on large scales and within galaxies.

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The Galaxy's supermassive black hole is a hundred times closer than any other massive singularity. It is surrounded by a highly unstable gas disk so why is the black hole so peaceful at the present time? This mystery has led to a flurry of models in order to explain why Sgr A* is radiating far below (1 part in 108) the Eddington accretion limit. But has this always been so? Evidence is gathering that Sgr A* has been far more active in the recent past, on timescales of thousands of years and longer. The bipolar wind discovered by MSX, the Fermi gamma-ray bubbles, the WMAP haze, the positronium flash confirmed by INTEGRAL, are indicative of something truly spectacular in the past. But when and how did this happen? We present new evidence that the Galactic Centre was a full blown "active galaxy" just a few million years ago. We discuss the most likely scenario for this incredible event which can be seen today imprinted across the Galaxy.

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In my talk I will present and discuss recent results from high-resolution simulations on the formation of the first galaxies and how these influence their environment. I will take a close look at how black holes will be seeded in such an environment and how the escape fraction of ionizing photons from galaxies evolves. Results from these simulations have profound implications for future observational missions with e.g. the James Webb Space Telescope and I will discuss these.

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The next generation of 40 m class Extremely Large Telescopes (ELTs) are currently under construction. These vast instruments will enable new discoveries in all areas of astronomy and push forwards the boundaries of human knowledge. They will look further back in space and time to explore the early universe and shed light on unanswered questions such as dark matter and dark energy. They will discover and characterise extra-solar planets and potentially find habitable, or even inhabited, worlds. To fulfil these ambitious objectives these giant telescopes will be equipped with highly sophisticated adaptive technologies in order to counteract the detrimental effects of the Earth’s atmosphere. The characterisation of atmospheric optical turbulence is critical for advanced optical astronomical observations. This includes using data from Adaptive Optics (AO) systems, dedicated auxiliary instrumentation as well as forecasts from numerical models of the Earth’s atmosphere. Exploiting this hybrid approaches enables us to determine the vertical profile of the turbulence strength, velocity, outer scale as well as the local turbulence contained in the telescope dome. This detailed knowledge is vital for wide-field AO systems which are particularly sensitive to the vertical structure of these atmospheric parameters and for highly-complex systems such as extreme AO, where the varying atmospheric parameters have a significant impact on performance. Atmospheric turbulence characterisation is therefore required for modelling, monitoring and optimising AO instrumentation, enabling efficient operation of current sophisticated instrumentation systems as well as the future Extremely Large Telescopes.

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M31 is the nearest large galaxy for which we have a dust-free multi-wavelength picture of its central regions. It presents some puzzles. The inner few parsecs are dominated by a double nucleus, which is most naturally explained by Tremaine's (1995) model of an eccentric disc of old stars around a supermassive black hole. A more recent surprise is the discovery of a very compact cluster of young stars around the black hole. I review ongoing work on the construction of a coherent picture of this system and compare it to the clusters found at the centres of other nearby galaxies.

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