Understanding the Cosmological Context of the Milky Way and its Neighbors

Galaxies in Observed and Simulated Universes

We see galaxies in the sky, but cannot see the dark matter clumps surrounding them. However, we can simulate them as they form in a model Universe. In this video we show how good the agreement is between the observed distribution of galaxies in the SDSS sky survey, and the predicted distribution of model galaxies associated with dark matter halos in the Bolshoi simulation. It's hard to tell them apart!

Statistics of Satellite Galaxies Around Milky Way-Like Hosts
Busha, Wechsler, Behroozi, Gerke, Klypin, and Primack
2011, ApJ, 743, 117

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How typical are the satellites of the Milky Way?

We are interested in the cosmological context of the Milky Way -- is it a special galaxy in any way? We found thousands of galaxies like it in the SDSS sky survey, and also thousands of matching halos in the Bolshoi simulation, and asked, how many have neighbours like the Magellanic Clouds? In both the real and simulated Universes we find that roughly 5% of Milky Way-like galaxies have 2 satellites like the Magellanic Clouds -- our galaxy is a bit unusual!

How Common are the Magellanic Clouds?
Liu, Gerke, Wechsler, Behroozi, and Busha
2011, ApJ, 733, 62

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The Formation of the Milky Way and its Neighbors

How did our galaxy form, and and when did its neighbors arrive? We found all the dark matter halos in the Bolshoi simulation that had subhalos with speeds, distances and masses that matched the Magellanic Clouds, and then visualized one of them to show what the Milky Way's development may have been like. The Magellanic Clouds likely arrived together, recently!

The Mass Distribution and Assembly of the Milky Way from the Properties of the Magellanic Clouds
Busha, Marshall, Wechsler, Klypin, and Primack
2011, ApJ, 743, 40

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This research was funded by the National Science Foundation and the Department of Energy, and used computing resources at SLAC National Accelerator Laboratory and on the NASA Advanced Supercomputing Pleiades computer at NASA Ames Research Center. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the Department of Energy, SLAC or Stanford.