The Illustris project: A large cosmological simulation of galaxy formation(illustris-project.org)
illustris-project.org
The Illustris project: A large cosmological simulation of galaxy formation
http://www.illustris-project.org/about/
2 comments
The Nature paper mentions that past simulations were unable to create the current population of disk galaxies (e.g. Andromeda, Milky Way).
They say "The culprit was an angular momentum deficit leading to too high central concentrations, overly massive bulges and unrealistic rotation curves." [0]
Any idea why these older sims wouldn't create the correct angular momentum in late-type galaxies?
[0] http://www.nature.com/nature/journal/v509/n7499/full/nature1...
They say "The culprit was an angular momentum deficit leading to too high central concentrations, overly massive bulges and unrealistic rotation curves." [0]
Any idea why these older sims wouldn't create the correct angular momentum in late-type galaxies?
[0] http://www.nature.com/nature/journal/v509/n7499/full/nature1...
> Any idea why these older sims wouldn't create the correct angular momentum in late-type galaxies?
My understanding from seeing talks this group has given is the culprit was the same effect I mentioned. If the fluid instabilities aren't properly handled, gas flowing onto galaxies stays cold and flows into the centers of galaxies [0], which results in less angular momentum because much of the material is at small radii. Correctly computing the fluid behavior results in gas not plunging directly to the centers of galaxies and instead building up at somewhat larger radii. For a given rotation speed, a larger galaxy will have higher angular momentum, so that's the sense in which their simulation improves on things.
[0] - This behavior has been called "cold flows" or "cold mode accretion" and was seen in simulations, but hasn't had direct observational support.
My understanding from seeing talks this group has given is the culprit was the same effect I mentioned. If the fluid instabilities aren't properly handled, gas flowing onto galaxies stays cold and flows into the centers of galaxies [0], which results in less angular momentum because much of the material is at small radii. Correctly computing the fluid behavior results in gas not plunging directly to the centers of galaxies and instead building up at somewhat larger radii. For a given rotation speed, a larger galaxy will have higher angular momentum, so that's the sense in which their simulation improves on things.
[0] - This behavior has been called "cold flows" or "cold mode accretion" and was seen in simulations, but hasn't had direct observational support.
Interesting. Thanks very much for the explanation.
I'm fascinated by the distinct types of structures that gravity and other forces create at such large scales. The really zoomed-out views of the universe remind me of neurons in a microscopic view of the brain.
When I was researching this stuff last year, I tried to use the Millenium Simulation (the world's largest n-body simulation at the time, 2 billion cubic light-years) to visualize this effect using webgl, but wasn't quite satisfied with the result [1]. Thanks to Illustris I've found out that one of the researchers on the project has created several excellent visualizations that seem to use some of the techniques from the larger simulation. They are worth taking a look if you're interested in visualization/simulation or how galaxies form [2].
[1] http://www.asterank.com/galaxies/ [2] https://www.cfa.harvard.edu/~dnelson/#tab-5
When I was researching this stuff last year, I tried to use the Millenium Simulation (the world's largest n-body simulation at the time, 2 billion cubic light-years) to visualize this effect using webgl, but wasn't quite satisfied with the result [1]. Thanks to Illustris I've found out that one of the researchers on the project has created several excellent visualizations that seem to use some of the techniques from the larger simulation. They are worth taking a look if you're interested in visualization/simulation or how galaxies form [2].
[1] http://www.asterank.com/galaxies/ [2] https://www.cfa.harvard.edu/~dnelson/#tab-5
[0] http://www.nature.com/nature/journal/v509/n7499/full/nature1...
[1] http://arxiv.org/abs/1405.1418
[2] Previous work used either a fixed mesh with adaptive refinement for higher-resolution or a "smoothed particle hydrodynamics" scheme where particles are used to simulate fluid flows. Both schemes have advantages and disadvantages, but the claim is that this moving mesh code ("Arepo") does the best job of treating fluid instabilities. The paper describing the new code is at: http://dx.doi.org/10.1111/j.1365-2966.2009.15715.x