#streams2015, day 1

I am at the Stellar Streams in the Local Universe meeting at Ringberg Castle. The meeting is small and workshop-like, so we are trying various experiments. One is to keep a running, completely public web document where everyone is encouraged to take notes on the talks and sessions. The first day was extremely lively. Here are some unfair and impressionistic thoughts:

Bovy opened the meeting, with his summary of the scientific subject of stellar streams in the Milky Way Halo, which range from dynamical modeling of the Milky Way to inferring the dark-matter and star-formation properties of low-mass galaxies.

I always think of the dynamical modeling, and rarely the galaxy evolution, so it was great to have Kathryn Johnston back up Bovy with the point that while we think of the Milky Way as being its own unique and bespoke object, there are enough collapsed, star-hosting overdensities disrupted in our halo that they probably constitute a relatively fair sample of small objects in the Universe. That is, we can do cosmology in our own halo (duh!). She also showed that the stream-to-shell ratio can be a cosmological test and speak to these questions, and she included a quantitative definition of "shell" and "stream"!

In the question period after a talk by Andrew Cooper (MPA) about simulations, he was asked whether in the outer halo the distribution of stars would follow the distribution of dark matter. This is a great question and idea, since both the stars and the dark-matter particles in those outer reaches are just test particles coming in. He said that they don't have an answer yet, but it looks likely that the stellar distribution is only a weakly biased version of the dark-matter distribution. That would be awesome.

Brendan Griffen (MIT) showed the Caterpillar suite of cosmological simulations of Milky-Way-like galaxies. This project is very simple, very well conceived, and producing very valuable tools.

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