Division of Theoretical Astronomy, National Astronomical Observatory of Japan

Web Release

The world’s most extensive simulation of the Milky Way galaxy


An international research team including Jeroen Bédorf, Simon Portegies Zwart (Leiden University, the Netherlands), Michiko Fujii (NAOJ, Japan) and others developed a new application “Bonsai” for numerical simulations of galaxies. Using this, they performed the world’s most extensive simulation of the Milky Way galaxy using 18600 GPUs. Around 240 billion particles are used in this simulation, and it provides detailed enough data for direct comparison to the observed stars in the Milky Way. In addition, the simulation achieved a computational speed of 24.77 Pflops (Peta Floating-point Operations Per Second), which is currently the world record. Because of these results, the research team is one of five finalists nominated for this year’s Gordon Bell Prize.

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“24.77 Pflops on a Gravitational Tree-Code to Simulate the Milky Way Galaxy with 18600 GPUs” by Jeroen Bédorf, Evghenii Gaburov, Michiko S. Fujii, Keigo Nitadori, Tomoaki Ishiyama, Simon Portegies Zwart, 2014, MACM/IEEE conference on Supercomputing (SC14), New Orleans, Louisiana, USA, Nov. 2014
Michiko Fujii([personal website])

Research Highlights

Revealing Large Amounts of Dust and Unusual Extinction Curves in the Early Unvierse


There are many pieces of evidence that the extinction curves of quasars at redshifts above z=5 are different from those at low-z quasars and that a huge amount of dust is present in their host galaxies. These indicate that the early interstellar medium was rapidly enriched with dust grains, whose properties are quite unusual.
We investigate the evolutions of dust content and extinction curve in a high-z quasar, based on the state-of-the-art dust evolution model that takes account of grain size distribution. We show that the massive amounts of dust and the peculier extinction curves in high-z quasars can be naturally explained if a large fraction of the interstellar medium is in dense molecular-cloud phases, where efficient grain growth and coagulation occur. We also find that the major composition of carbonaceous dust in high-z dusty galaxies is amorphous carbon rather than graphite. These results indicate the differences in the properties of dust and in the condition of the interstellar medium between low-z and high-z galaxies.
The figure shows calculated UV extinction curves at t = 1 Gyr. The dotted, thick solid, and dashed lines show the results for the mass fraction of the molecular-cloud phase, 0.5, 0.7, and 0.9, respectively. The hatched region is the range of the extinction curve for the high-z quasar J1048+4637 at z = 6.2 (Maiolino et al. 2004). For comparison, the SMC extinction curve is drawn by the thin solid line.
Evolution of grain size distribution in high-redshift dusty quasars: integrating large amounts of dust and unusual extinction curves by Takaya Nozawa, Ryosuke S. Asano, Hiroyuki Hirashita, Tsutomu T. Takeuchi, 2015, MNRAS Letters, 447, L16-L20
[ADS] [arXiv]
Takaya Nozawa([personal website])