High Performance Computing in Science and Engineering '09 (PDF)

"Numerical Models for Emission Line Nebulae in High Redshift Radio Galaxies (S. 3-4)

Summary. We examine models for line-emitting gas nebulae around powerful radio galaxies in the early universe. The models assume that either the emitting gas clouds are embedded in the shocked ambient gas and driven outwards with it or that they are created and sustained by multi-phase turbulence in the jet cocoon. For this, we perform jet simulations with realistic density contrasts on large scales and on typical activity time scales of several ten million years. The employed magnetohydrodynamics code NIRVANA has been optimized for the NEC SX machines in the previous years and now runs very e?ciently on the SX-6 and SX-8, allowing us simulations both in axisymmetry and full three dimensions. Future simulations on the SX-9 will bene?t signi?cantly from the increased number of shared memory processors per node for the axisymmetric runs, where an MPI-parallelization is generally ine?cient for our setup due to communication overhead.

1 Introduction

Extragalactic jets are amongst the most spectacular phenomena in astrophysics: These collimated beams of dilute but highly energetic plasma are formed in the environs of active black holes, on scales of milliparsecs3 with speeds very close to the speed of light, and propagate far outwards, eventually leaving the galaxy and pushing through the intergalactic gas at hundreds or even thousands of kiloparsecs.

Over these more than seven orders of magnitude in length, they remain collimated and deposit a large fraction of their huge kinetic energies of ∼ 1039 watts on the ambient gas. Yet, due to their low densities relative to the gas in galaxy cluster, they expand only slowly and reach their largest sizes only after several tens of millions of years. While these objects have been discovered already more than 50 years ago as double radio sources, only improving observational

Aus den Rezensionen:“Obwohl auch aus finanziellen Gründen eigentlich auf einen engen Kreis von Forschern beschränkt, ist die Simulation mit Supercomputern bzw. deren Resultate kaum mehr aus unserem Alltag wegzudenken - Stichwort numerische Wettervorhersage. ... Ein wissenschaftliches Buch, das den aktuellen Stand des vielfältigen Einsatzes von Supercomputing in Deutschland präsentiert.“ (in: Bulletin SEV/VSE, February/2010, S. 87)