IllustrisTNG: a Universe in a Box

Dylan Nelson, Heidelberg University

Video Recording

Abstract:

Recently it has become possible to numerically simulate large, representative volumes of the Universe. These cosmological (magneto)hydrodynamical simulations solve for the coupled evolution of gas, dark matter, stars, and supermassive black holes interacting via the coupled equations of self-gravity and fluid dynamics, all within the context of an expanding spacetime.

The IllustrisTNG simulations are the current state-of-the-art in this context. They simultaneously resolve tens of thousands, to millions, of individual galaxies - with properties and characteristics in broad agreement with observational data of real galaxy populations. This enables many theoretical studies on galaxy formation and evolution, as well as large-scale structure and cosmology.

These calculations are challenging. Our largest runs to date evolve ~1e10 resolution elements for >1e7 timesteps, requiring ~100M core hours, parallelized on up to ~100k CPU cores, and typically run on Top10 HPC systems. Our numerical backbone is the AREPO "moving-mesh" code, which adopts a finite-volume type approach to solve the equations of ideal MHD on an unstructured, spatially and temporally adaptive discretization of space provided by a Voronoi tessellation. The enormous dynamic range of the problem, in both space and time, requires the use of a hierarchical, individual time stepping scheme. Simultaneously, key astrophysical phenomena always occur -below- the resolution scale, requiring extensive "sub-grid" models to capture processes such as radiative cooling, star formation, supernovae explosions, black hole dynamics, growth, and feedback energy.

Bio:

Dylan Nelson is currently an Emmy Noether Research Group Leader at the Institute for Theoretical Astrophysics, within the Center for Astrophysics (ITA/ZAH) of Heidelberg University, Germany. Previously he was a postdoctoral fellow at the Max Planck Institute for Astrophysics (MPA) in Munich, Germany. Five years ago he completed his PhD in astrophysics at the Center for Astronomy (CfA) at Harvard University, working with Lars Hernquist. His interests include theoretical modeling of cosmological gas accretion, the circumgalactic medium, the baryon cycle, and energetic feedback processes, particularly in their connections to the formation and evolution of galaxies and galactic structure over cosmic time.