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Department of Astrophysics

Galaxy and Star Formation

Galaxies and the stars within them make up the "bright" side of the Universe. Weather permitting, thousands of stars, as well as several galaxies, are visible to the naked eye every night. These numbers increase dramatically with the help of powerful telescopes. Recently, the Gaia mission compiled stellar catalogs containing over a billion stars, while the Sloan Digital Sky Survey (SDSS) imaged hundreds of millions of galaxies.
Since antiquity, people have marveled at the sight of stars and galaxies and speculated on their origins. It was not until about a century ago, however, that scientists fully grasped the extraordinary nature of galaxies. After measuring their distances accurately, it became clear that galaxies were not nebulae of gas residing within the Milky Way as previously assumed, but rather that they are extragalactic systems on par with the Milky Way.
Since then, the study of galaxies has become an integral part of astrophysics for a number of reasons. First, galaxies are cosmological laboratories that probe physics in extreme environments. ‘Cosmic experiments' carried out by galaxies include the ejection of large amounts of matter in high-velocity galactic outflows, interactions and mergers between galaxies, and the suppression of star formation in massive galaxies, to name a few examples. Secondly, galaxies are the shining beacons that are observable out to large distances and, hence, can be used to map out the Universe. For instance, astronomers use galaxy catalogs to probe the distribution of dark matter and the growth of structure in the Cosmos. Finally, the study of galaxies across cosmic time allows astrophysicists to better understand the origin and history of our own parent galaxy, the Milky Way.
Despite significant progress in understanding how galaxies and stars form over the last decade, there are many questions of paramount importance that have yet to be answered. These questions include:
•    Which physical processes regulate star formation in galaxies?    
•    Why, when, and how do many galaxies shut down star formation altogether?    
•    What is the formation history of galaxies like our own?    
•    How did the first galaxies form and what are their properties?    
•    How is the growth and enrichment of galaxies connected to gas accretion from their cosmic environments?    
•    What is the physical nature of the observed link between galaxy growth and the growth of the supermassive black holes at their centres?    
•    How are powerful outflows from galaxies generated and which role do they play in galaxy evolution?
At ICS we study stars and galaxies with the help of advanced computational models. Numerical simulations complement observational efforts and provide detailed insights into the physical processes that underlie the formation and evolution of galaxies and stars. High-resolution simulations undertaken at ICS explore the early stages of galaxy formation and map their properties to observation space, resulting in data that can be directly compared with observations made with the Hubble Space Telescope (HST), the Atacama Large Millimeter Array (ALMA), the James Webb Space Telescope (JWST), and the planned Square Kilometre Array Observatory (SKAO). Given the high computational demands of current state-of-the-art simulations in galaxy and star formation, we continuously refine our massively-parallelized codes and make heavy use of supercomputers, e.g., at the Swiss National Supercomputing Centre. In addition, several of our institute members are involved in a variety of observational efforts to probe the formation and evolution of stars and galaxies.


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